I agree with most of your choices, but the methodology behind some of them is curious at best. For example, people should dump Sarkhan because "if it wasn't strong enough for Standard, it won't be good in Modern or Legacy." While this may be true in this case, there are plentiful examples of cards that did nothing in their respective Standard environment that are mainstays of decks in both formats (Etched Champion and Memnite were unplayable in both Scars Standards but are 4-ofs in Modern Affinity, both Eldrazi lands were unplayable in Standard but are now warping Modern like few cards ever have, Crucible of Worlds never did anything in Standard but is a Legacy staple, etc.). Just seems short-sighted to ditch stuff because it wasn't Tier 1 in its Standard environment.
Also, while I agree that Ugin should drop off a little bit over the next month or two, I think he's going to go WAY up in relatively short order (like, within a year or less of rotation). Remember, there are plenty of cards that see little to no competitive play that hold value exceptionally well (classic example: Glimpse the Unthinkable), and planeswalkers in particular are highly-sought casual superstars (freaking Tibalt is still $3 TCG mid!). Ugin is going to be the Holy Grail in this regard (can go in any deck, is a badass dragon, really powerful, only one printing); add onto that its playability in Tron and you're looking at a card that could hit $50 by mid-2017.
...that said, I'm absolutely going to be adding this to my Melek deck and abusing the hell out of it with time magic, because I'm a bad person.
2. Black EDH decks are drooling over Bontu's Last Reckoning, but in any other constructed format I just don't see it. How many formats allow you to essentially take a turn off after wrathing? Add in that it does nothing to hit Gideon or HoK and it seems like this barely lets you stem the bleeding at all. MAYBE against a vomit-your-hand deck in Modern like Elves or Affinity, but I'm not sure what shell it would slot into for that.
3. Samut is hot garbage, for two reasons. One, while Tooth and Nail as a planeswalker ultimate fits nicely and is probably long overdue, her other abilities are weak as hell. I mean, Forked Bolt? Really? Two, her sparking means that Djeru probably won't, which means that instead of an interesting character at a moral crossroads with B/W leanings, we get another generic R/G "I'm cool because I'm a rebellious loose cannon" cardboard cutout for the Gatewatch. While my hope is that the last Story Spotlight shows Bolas eating her, I won't hold my breath.
Counterpoint: the interaction with the new Gideon is bad and they should feel bad. Platinum Angel didn't even exist the last time Final Fortune was legal; putting a three-mana Angel effect into Standard with this, where the Fortune equivalent also effectively counters any removal for the effect, seems short-sighted. That said, I'm still very glad this card exists. It just makes me wish even more that Gideon of the Trials didn't.
They're not putting an instant-speed graveyard tutor/delirium enabler into this Standard, especially when the most vocal aspects of the player base have been *****ing about the lack of graveyard hate for three sets now. Sorry.
On topic: it's a good spread of powerful stuff, but nothing in green is admittedly a bit surprising, particularly when this might be the most perfect set ever for the biggest troll Masterpiece of all time. There's still plenty of room for interesting things in the next set (keeping fingers crossed for Bolas-themed Damnation), and I'm sure one of them will be something like Natural Order, which seems to fit the "only the strong survive" theme of the plane.
On topic: I figured once the fetches were announced that this was ruled out by virtue of the fetches devouring EV. Who would have guessed that Wizards was serious this time about making Modern more affordable? What are we at now, three bulk rares out of approximately 40 rares and mythics revealed? That's nuts!