Wyll's dialogues in Act III do get a little strange at times. Some trigger multiple times, others seem to fully miss the point of what's going on. Since I sailed without a map to avoid spoilers, I thought maybe it's because I approached some quests from more than one end, but it's all over the place.
A big +1 on a happy ending for the Hellion's Heart.
I also expected Saving the Gondians, collecting Enriched Infernal Iron and something in the Steel Watch Foundry or the House of Hope (Maybe Stygian or Canian ice?) would do the trick, but Baldur's Gate isn't Hollywood. Karlach ended up becoming the wielder of the prism in my definitive playthrough. While it was fun to have a mind flayer in the battle, I would have preferred Omeluum.
This will most likely be a job for modders, though, unless it's already part of an upcoming warmfix.
Larian has moved on from BG3.
I also get your point about trying to convince Therezzyn that you're not the druids they're looking for, but since I played a Githyanki, it actually worked for me this way. No negotiation! She probably wouldn't take a non-Githyanki's word for it, and Githyanki reach the end of diplomatic efforts rather quickly.
