The gold standard up until the end where the game makes you stand there and watch him run away as his face starts melting (but that's for a different thread). They all get shafted in one way or another, even god's favorite princess who is so relevant to the plot but didn't get a single line to say in any of my endings.
Fwiw it's not his end yet if you romance him, so even with how bad that scene is, he got by far the best romance arc.
I think EA Wyll was better. I was really looking forward to seeing the extent of his hate for goblins and his other flaws.
Wyll is way too perfect as it is now because you never truly get to question him about his choices. It would've made more sense if he made the pact with Mizora because he felt too weak in general, not to save some world-ending plot as a teenager. And it would've made his sacrifice at the end have more impact as well because he'd turn back to being 'too weak'. Karlach has a similar issue. The other companions all have some sort of flaw, forced (Shadowheart), semi-forced (Astarion), or just self-imposed (Gale, Lae'zel).
Agree on the exploration of self-sacrifice and how much of himself he wants to lose to be the hero. A more realistic confrontation with his father. For companion interactivity he could have more thoughts on traveling with a vampire and a Shar worshiper.
I do like the confrontation with his father. You get to talk to him together, he acknowledges Wyll's deeds as good, and I doubt he'd ask Wyll to become Grand Duke and rule the city if he thought Wyll was still under Mizora's contract (though I never played the permanent contract version out, so feel free to correct me if I'm wrong). Though, afaik, you don't get to talk about your romance with him, which is a massive oversight - just another to add to the list of romance options that should've existed. Story ending spoilers for another companion with parents:
For all the flaws your confrontation with Shadowheart's parents has (you don't get to talk about them, or to them together with her, or with her at all after saving them really, she has nothing left to say), at least they do acknowledge your romance.
As for his romance, I like how it starts, but I can never make myself finish it because Act 3 exhausts me and Wyll is involved in the least interesting parts of it.
I think the only two companions that have a remotely decent romance in act 3 are Karlach and Astarion. Karlach needed it, Astarion is what every other companion should be like, but none are. The others have so much potential but it just doesn't play it out. Same dialogue, romanced or not, everywhere.
That said, I don't like how Wyll's romance starts. I like the idea of it, but it just doesn't play out well to me. Wyll seriously needs some kind of romance check. I had no idea I was still able to romance him throughout act 2 until his dance triggered out of the blue. and it appears unrelated to your decisions in act 1. Just purely approval based, which means his romance doesn't actually start until act 2.