ECD and U8in are perm solutions to Uro. Krasis is more difficult to deal with. I'm also playing Bo1 so my sideboard is just a wishboard for Fae (Grafdigger's Cage ect). I'm also in Platinum, and I'm sure my opponents are easier than yours (exe, guy Duress' U8in while my ECD is at lvl2 and I had no targets in GY). I think my 4/4 flying tokens help to close out games quicker. Outlaw's Merriment sounds way to slow, I run 6 5-drops, 1 U6in and 2 U8in at my top end. I agree with you though, Sultai is a tough cookie to crack
side note - Do you use Field of Ruin? It can function as a forced shuffle after you use Aether Gust (I think MBM taught me that). They will eventually draw it again though. I run 2 Gust and Teferi can toss them if they're dead cards
Played a bit more of the matchup, I think Sultai is definitely favored against UW. ECD is not a good answer to Uro because of how expensive it is, but more importantly, Krasis is a huge haymaker and Agonizing Remorse / Thought Erasure destroy control hands. If the UW deck ever runs out of counterspells (or the hand destruction forces that to happen) then Casualties of War is a huge blowout especially against the Yorion builds that are relying on enchantment removal. Even the removal spells & maindeck Aether Gusts aren't truly dead because they can be discarded to Teferi's +1 (who loots twice a turn too).
In one game I easily outvalued a UW deck through their 8-card hand after I mulliganed too. I got my first 3-for-1 with Krasis for 4, drawing 2, then used Thought Erasure to remove their ECD to resolve a Nissa. That forced them to tap low on their turn, which let me escape Uro, they played Shatter which was effectively another 3-for-1 (since I drew a card with Uro already, and then drew another one with Shatter), etc.
On another note: I have no idea what this deck is
https://www.mtgtop8.com/event?e=27045&d=412531&f=ST. Anyone understand the weird card choices, going as deep as Topple the Statue (??)