I'm not going to lie. If CV were legal I would play under the assumption that it were in every five color deck and play appropriately. And if that means thingame like removing their land when given the opportunity or killing their general just because I can, I wouldn't feel bad about it.
Do you play under the assumption that every black green deck is going to tooth and nail for mike and trike? Or that every blue deck is going to win the game if they hit 10 mana for omniscience?
We can't use arbitrary irrational behaviour for the banlist.
I am with Cryogen on this one. If CV were legal, I would assume that every 5C deck is playing it and I would play the rest of the game under than assumption because of the difficulty in dealing with it. If the argument is that CV is fine because every color can deal with it by blowing up lands (Red/Green/Strip Mine variants), getting rid of the general (Black/White/Red) or countering CV itself (Blue mostly) then if I am not playing Blue (since it really does all 3 things to stop CV) I am going to actively make sure the 5C player doesn't have all 5 basic land typesor their general.
Since a lot of LD effects are sorcery speed, I can't just respond to CV to blow up a land. Removing the general is a little easier to do in response to CV, but if my removal is countered, I lose. I will do what I can to make sure their general and/or lands don't stick around throughout the game.
Except it doesn't take 10 cards. It takes 5: your general, 3 lands with basic land types, and Coalition Victory itself (which you mentioned further down). Prismatic Omen isn't needed and its a bit disingenuous to suggest mana ramp cards should be included in that count since those cards are going to see play anyway. Other than needing 8 mana, you just ramp into Tropical Island, Badlands, and Scrubland (or the Shock Land equivalents/mix and match of duals), cast your general, tutor out Coalition Victory, and win. 8 mana isn't that hard to come by in EDH.
The fact that it requires such little investment (both in game and with regards to deckbuilding) is a problem. I agree that other instant win combos can be just as unfun but this one seems like it has fewer ways of stopping it. In the example of Kiki/Exarch, if you exile or kill Kiki, the combo stops and it is harder to do it again. If you Fog, nothing happens. If the setup is countered, nothing happens. Temple Bell/MoM can be interrupted (kind of) with artifact/enchantment hate, (such as Krosan Grip), counter magic, etc. It also takes a bit more to get the combo online and it still requires and additional win-con (drawing your deck isn't enough) and that win-con can be dealt with too (Laboratory Maniac can be removed for example).
Niv-Mizzet is a good example though as it is the one that is the closest to Coalition Victory since it revolves around 1 card and the general so it is harder to stop. It does take a little setup but it also requires you to run Niv-Mizzet as your general and you are running colors that make it tougher to tutor up an enchantment. I think those are enough restrictions that it ends up being fine.
So, I think you misunderstand the difficulty in winning with Coalition Victory. It is much easier than Primal Surge (requires somewhat severe deckbuilding restrictions) or Enter the Infinite (requires 12 mana, 4 of which is U and an actual win-con once you draw your deck). Coalition Victory just goes into every 5 color deck because it takes up a total of 1 card slot. As long as the deck is running Duals/Shocks/Battle Lands, the entire suite of cards necessary for winning off of Coalition Victory is already there. There is no thought in the decision and it becomes an almost auto-include for nearly every 5 color deck. The decks also have access to everything to make the win work and none of the cards need to be added specifically for CV. Tutors are already good. Eternal Witness and Regrowth are already good and they get back Coalition Victory. Counterspells are good and they protect the "combo".
Are the other combos you listed unfun? Absolutely (though not all will necessarily share that sentiment). I just don't think the existence of other infinite combos (which can never be entirely removed from the game) is enough to justify the unbanning of Coalition Victory.
Since a lot of LD effects are sorcery speed, I can't just respond to CV to blow up a land. Removing the general is a little easier to do in response to CV, but if my removal is countered, I lose. I will do what I can to make sure their general and/or lands don't stick around throughout the game.
The fact that it requires such little investment (both in game and with regards to deckbuilding) is a problem. I agree that other instant win combos can be just as unfun but this one seems like it has fewer ways of stopping it. In the example of Kiki/Exarch, if you exile or kill Kiki, the combo stops and it is harder to do it again. If you Fog, nothing happens. If the setup is countered, nothing happens. Temple Bell/MoM can be interrupted (kind of) with artifact/enchantment hate, (such as Krosan Grip), counter magic, etc. It also takes a bit more to get the combo online and it still requires and additional win-con (drawing your deck isn't enough) and that win-con can be dealt with too (Laboratory Maniac can be removed for example).
Niv-Mizzet is a good example though as it is the one that is the closest to Coalition Victory since it revolves around 1 card and the general so it is harder to stop. It does take a little setup but it also requires you to run Niv-Mizzet as your general and you are running colors that make it tougher to tutor up an enchantment. I think those are enough restrictions that it ends up being fine.
So, I think you misunderstand the difficulty in winning with Coalition Victory. It is much easier than Primal Surge (requires somewhat severe deckbuilding restrictions) or Enter the Infinite (requires 12 mana, 4 of which is U and an actual win-con once you draw your deck). Coalition Victory just goes into every 5 color deck because it takes up a total of 1 card slot. As long as the deck is running Duals/Shocks/Battle Lands, the entire suite of cards necessary for winning off of Coalition Victory is already there. There is no thought in the decision and it becomes an almost auto-include for nearly every 5 color deck. The decks also have access to everything to make the win work and none of the cards need to be added specifically for CV. Tutors are already good. Eternal Witness and Regrowth are already good and they get back Coalition Victory. Counterspells are good and they protect the "combo".
Are the other combos you listed unfun? Absolutely (though not all will necessarily share that sentiment). I just don't think the existence of other infinite combos (which can never be entirely removed from the game) is enough to justify the unbanning of Coalition Victory.