I have a hard time believing that a starke of rath deck needs "one that's really tight and competitive enough for everything but a cEDH table" to beat it. When you say theft, red doesn't have a lot of permanent steal effects, is he just stealing creatures until end of turn and killing them with starke? If so, obviously some well-timed targeted removal on starke would nullify that strategy pretty easily. And if you're playing Bruna, you could just kill him eot before playing her, so he can't kill her with his activated ability. Sigarda would also be fine, though.
Grenzo doomsday sounds way scarier than starke to me. Maybe you could elaborate? Good grenzo doomsday decks are usually trying to combo kill the table around turn 4. So that seems way more concerning than starke of rath. Although most of those combos are disruptable with a single piece of targeted removal, so it's definitely beatable with a half-decent control deck. Are the Ux control decks stopping Grenzo?
I'm just really confused about this meta that you've got a legit cEDH deck, and Ux control decks (generally strong)...but starke of rath is the deck that you're worried about? Sigarda seems like an easy win vs starke, but I'm just confused why Starke is the major concern here.
When you lose games, how does it generally happen? What is disrupting your strat, and what is the winner using to win?
wildcard vote, but you might try krav+regna partners. They're both strong cards, and you've effectively got twice as many commanders to kill. Plus with cards like tel-jilad stylus you can use them to tutor each other if they die.
It's a little hard for me to be too sure without knowing your meta better, but in general I think Bruna is probably on the right track. White/blue is, imo, an excellent color combo for control if built and played well - between counters, targeted removal for any permanent type, and board wipes you have all the tools you need to keep the game under control until you can deploy and protect your win condition. Bruna does necessitate a certain number of slots for auras to be effective, but that's probably not too big of a deal. Make sure you have a lot of ways to give her haste too. Jenara, on the other hand, really doesn't need any support, you can just jam her into a draw/go control deck and she'll do just fine (although of course a little protection and equipment wouldn't hurt).
I still think that, on average, trying to win via commander damage is not a very effective way to win frequently - but of course there are exceptions. Bruna can 1-hko people pretty easily, but be careful not to overplay your hand, don't go for the kill until you can protect it. Jenara, with a low cost and inevitability is more of an incidental wincon for the same kind of heavy control deck as my Phelddagrif build (Phelddagrif is much better imo, but jenara is more straightforward and probably doesn't drag out the game as long as Phelddy). Haven't looked at the primer so I can't comment on its accuracy, but I think if you're having trouble with blunt strategies then the way to go is something a little more subtle, and a slower, more political control build is probably your best bet. I tend to find that the more i keep politics in mind as I build and play the higher my win rate is. Even my budget phelddy build has a solid 70%+, I'm assuming Jenara could achieve something similar. Play skill is pretty critical though. Gotta be good at evaluating which threats to answer and which to let lie (or let other people answer).
As far as Sigarda, it's also hard to know without knowing your meta. Maybe it would solve your problems, but imo a fast voltron deck is a really uninteresting way to play the game. You try to build a threat as quickly as possible, and then you either beat people to death with it because they lack a way to interact with it, or they do have a way to interact and you're back to square one. Basically it's just very linear. If it ever actually becomes good, then it's really easy to counter it and play around it by running and holding answers for Sigarda. Basically the same problem as Nazahn, except that hexproof limits the number of answers that are effective - but even if you pull it off, I think it'll be kind of boring. Interactivity is the heart of a good game. As long as you aren't relying on speed to carry the day, you can afford to wait for the right moment to strike - something that I think bruna, with her enormous potential for burst damage, does a lot better. Wait for people to exhaust their answers on other threats, and keep up your own counters to protect her, and go for the win when people aren't prepared for it.
I'd build bruna either as sort of a pseudo-combo control deck, playing the control game until you swing for a hasty lethal against the biggest threat, with answers up for the other players, or build Jenara as a grindier control deck that plays a bit more politically. Bruna is probably easier to make effective, but I think they're both good options.
If you're winning so few games, I think the problem is your strategy, not your power level (well, maybe both). Voltron is not a good strategy if you want to win games, in my experience. It's telegraphed and easily dusruptable and slow, and draws proportionally more hate than other strats because it's so telegraphed.
Angel midrange, same deal. Medium sized flyers are not an effective strat.
I'd look towards either control and/or combo, or at least something a bit burstier and higher value.
Grenzo doomsday sounds way scarier than starke to me. Maybe you could elaborate? Good grenzo doomsday decks are usually trying to combo kill the table around turn 4. So that seems way more concerning than starke of rath. Although most of those combos are disruptable with a single piece of targeted removal, so it's definitely beatable with a half-decent control deck. Are the Ux control decks stopping Grenzo?
I'm just really confused about this meta that you've got a legit cEDH deck, and Ux control decks (generally strong)...but starke of rath is the deck that you're worried about? Sigarda seems like an easy win vs starke, but I'm just confused why Starke is the major concern here.
When you lose games, how does it generally happen? What is disrupting your strat, and what is the winner using to win?
wildcard vote, but you might try krav+regna partners. They're both strong cards, and you've effectively got twice as many commanders to kill. Plus with cards like tel-jilad stylus you can use them to tutor each other if they die.
EDH Primers
Phelddagrif - Zirilan
EDH
Thrasios+Bruse - Pang - Sasaya - Wydwen - Feather - Rona - Toshiro - Sylvia+Khorvath - Geth - QMarchesa - Firesong - Athreos - Arixmethes - Isperia - Etali - Silas+Sidar - Saskia - Virtus+Gorm - Kynaios - Naban - Aryel - Mizzix - Kazuul - Tymna+Kraum - Sidar+Tymna - Ayli - Gwendlyn - Phelddagrif 4 - Liliana - Kaervek - Phelddagrif 3 - Mairsil - Scarab - Child - Phenax - Shirei - Thada - Depala - Circu - Kytheon - GrenzoHR - Phelddagrif - Reyhan+Kraum - Toshiro - Varolz - Nin - Ojutai - Tasigur - Zedruu - Uril - Edric - Wort - Zurgo - Nahiri - Grenzo - Kozilek - Yisan - Ink-Treader - Yisan - Brago - Sidisi - Toshiro - Alexi - Sygg - Brimaz - Sek'Kuar - Marchesa - Vish Kal - Iroas - Phelddagrif - Ephara - Derevi - Glissa - Wanderer - Saffi - Melek - Xiahou Dun - Lazav - Lin Sivvi - Zirilan - Glissa
PDH - Drake - Graverobber - Izzet GM - Tallowisp - Symbiote Brawl - Feather - Ugin - Jace - Scarab - Angrath - Vraska - Kumena Oathbreaker - Wrenn&6
I still think that, on average, trying to win via commander damage is not a very effective way to win frequently - but of course there are exceptions. Bruna can 1-hko people pretty easily, but be careful not to overplay your hand, don't go for the kill until you can protect it. Jenara, with a low cost and inevitability is more of an incidental wincon for the same kind of heavy control deck as my Phelddagrif build (Phelddagrif is much better imo, but jenara is more straightforward and probably doesn't drag out the game as long as Phelddy). Haven't looked at the primer so I can't comment on its accuracy, but I think if you're having trouble with blunt strategies then the way to go is something a little more subtle, and a slower, more political control build is probably your best bet. I tend to find that the more i keep politics in mind as I build and play the higher my win rate is. Even my budget phelddy build has a solid 70%+, I'm assuming Jenara could achieve something similar. Play skill is pretty critical though. Gotta be good at evaluating which threats to answer and which to let lie (or let other people answer).
As far as Sigarda, it's also hard to know without knowing your meta. Maybe it would solve your problems, but imo a fast voltron deck is a really uninteresting way to play the game. You try to build a threat as quickly as possible, and then you either beat people to death with it because they lack a way to interact with it, or they do have a way to interact and you're back to square one. Basically it's just very linear. If it ever actually becomes good, then it's really easy to counter it and play around it by running and holding answers for Sigarda. Basically the same problem as Nazahn, except that hexproof limits the number of answers that are effective - but even if you pull it off, I think it'll be kind of boring. Interactivity is the heart of a good game. As long as you aren't relying on speed to carry the day, you can afford to wait for the right moment to strike - something that I think bruna, with her enormous potential for burst damage, does a lot better. Wait for people to exhaust their answers on other threats, and keep up your own counters to protect her, and go for the win when people aren't prepared for it.
I'd build bruna either as sort of a pseudo-combo control deck, playing the control game until you swing for a hasty lethal against the biggest threat, with answers up for the other players, or build Jenara as a grindier control deck that plays a bit more politically. Bruna is probably easier to make effective, but I think they're both good options.
EDH Primers
Phelddagrif - Zirilan
EDH
Thrasios+Bruse - Pang - Sasaya - Wydwen - Feather - Rona - Toshiro - Sylvia+Khorvath - Geth - QMarchesa - Firesong - Athreos - Arixmethes - Isperia - Etali - Silas+Sidar - Saskia - Virtus+Gorm - Kynaios - Naban - Aryel - Mizzix - Kazuul - Tymna+Kraum - Sidar+Tymna - Ayli - Gwendlyn - Phelddagrif 4 - Liliana - Kaervek - Phelddagrif 3 - Mairsil - Scarab - Child - Phenax - Shirei - Thada - Depala - Circu - Kytheon - GrenzoHR - Phelddagrif - Reyhan+Kraum - Toshiro - Varolz - Nin - Ojutai - Tasigur - Zedruu - Uril - Edric - Wort - Zurgo - Nahiri - Grenzo - Kozilek - Yisan - Ink-Treader - Yisan - Brago - Sidisi - Toshiro - Alexi - Sygg - Brimaz - Sek'Kuar - Marchesa - Vish Kal - Iroas - Phelddagrif - Ephara - Derevi - Glissa - Wanderer - Saffi - Melek - Xiahou Dun - Lazav - Lin Sivvi - Zirilan - Glissa
PDH - Drake - Graverobber - Izzet GM - Tallowisp - Symbiote Brawl - Feather - Ugin - Jace - Scarab - Angrath - Vraska - Kumena Oathbreaker - Wrenn&6
Angel midrange, same deal. Medium sized flyers are not an effective strat.
I'd look towards either control and/or combo, or at least something a bit burstier and higher value.
EDH Primers
Phelddagrif - Zirilan
EDH
Thrasios+Bruse - Pang - Sasaya - Wydwen - Feather - Rona - Toshiro - Sylvia+Khorvath - Geth - QMarchesa - Firesong - Athreos - Arixmethes - Isperia - Etali - Silas+Sidar - Saskia - Virtus+Gorm - Kynaios - Naban - Aryel - Mizzix - Kazuul - Tymna+Kraum - Sidar+Tymna - Ayli - Gwendlyn - Phelddagrif 4 - Liliana - Kaervek - Phelddagrif 3 - Mairsil - Scarab - Child - Phenax - Shirei - Thada - Depala - Circu - Kytheon - GrenzoHR - Phelddagrif - Reyhan+Kraum - Toshiro - Varolz - Nin - Ojutai - Tasigur - Zedruu - Uril - Edric - Wort - Zurgo - Nahiri - Grenzo - Kozilek - Yisan - Ink-Treader - Yisan - Brago - Sidisi - Toshiro - Alexi - Sygg - Brimaz - Sek'Kuar - Marchesa - Vish Kal - Iroas - Phelddagrif - Ephara - Derevi - Glissa - Wanderer - Saffi - Melek - Xiahou Dun - Lazav - Lin Sivvi - Zirilan - Glissa
PDH - Drake - Graverobber - Izzet GM - Tallowisp - Symbiote Brawl - Feather - Ugin - Jace - Scarab - Angrath - Vraska - Kumena Oathbreaker - Wrenn&6