Thor's change was utterly unmotivated and unearned. Why did he change? He got drunk in a bar and woke up a completely changed person. ??? He did absolutely nothing to prove himself worthy. Honestly, it took 4 or 5 movies for them to get Thor right. Thor! The single simplest of the Avengers.
Loki was... ...utterly lacking. He didn't feel like he had a motive at all. The most interesting version of Loki was... ...every other version of Loki in the Loki TV show. In Thor and Avengers he was just a mustache twirler. "I'm evil because I'm eeee vil. Bu wah ha ha haaaaa."
Winter Soldier would have been a way better intro to Cap than TFA. Why introduce the Howling Commandos if you're not even going to even give them names? How tough can a villain be if he's defeated in a 10-minute montage?
No, I think Thor had a pretty solid arc. He’s initially the golden boy, leader of the gang, heir to the throne, who both feels the weight of future responsibility and chafes at what he sees as his father’s age and weakness. That comes out very clearly in the confrontation that leads to his banishment.
“You are a vain, greedy, cruel boy!”
“And you are an old man and a fool!”
“Yes, I was a fool… to think you were ready. Thor Odinson, you have betrayed the express command of your king. You are unworthy of these realms, unworthy of your title, unworthy of the loved ones you have betrayed! I now take from you your power! In the name of my father and his father before him, I CAST YOU OUT!”
(This scene, when Odin literally strips Thor of his armour and cloak, mirroring the disgracing of Alfred Dreyfus, is killer.)
And Thor is abandoned, petulant, entitled; still a vain child who hasn’t processed what’s happened.
And then he cannot lift his hammer; his power rejects him and deems him unworthy. It would all have been OK if Mjolnir had accepted him for who he was.
And THEN Loki - his brother and confidant, whom he trusts implicitly - comes to him and does the Iago bit. Dad is dead, Loki is reluctantly king now; he’s sorry, but there can be no official forgiveness, even their mother won’t see Thor.
Only then does Thor, completely broken by his own failures (as he sees them), understand that it’s up to him to define himself, get up, and make the best of the rest of his possibly endless life. He takes it one day at a time. He starts to care about those around him and his new home. He starts to become worthy.
And I agree this part could have used more development, but sadly we didn’t have time. The final step to worthiness is when he takes on the Destroyer with nothing but mortal strength and skill, willing to sacrifice himself to protect even one other person. And then Mjolnir flies to his hand, like it’s been waiting all along.
I think it’s a great arc and one that shows up in every version of Thor since. Even in Endgame, when he’s broken again, he’s striving for worthiness, to do something good.
Equally, Loki has a good arc. He’s the younger less charismatic son - he gets it, he’s used to being the clever one who gets Thor out of trouble and making things work, he’s looking forward to being his vizier forever. But then Thor is exiled and he’s the heir, he’s not prepared, and then he discovers that he’s not Asgardian, he’s an enemy child adopted as a potential diplomatic resource for conquest. And he snaps - he hates himself, hates his Jotun lineage, decides to genocide the Jotun to eliminate everything he hates and take the throne (which is already within reach) by force and guile because that’s what a Jotun would do. He’s lashing out, no sense of self, all his wits doing nothing to help him process what’s happened.
It takes him ages to process this and he pretends to be a villain because that helps (and of course Thanos tortures him and will kill him if he doesn’t conquer Earth). And he is a villain - he kills and maims and threatens, he’s responsible for many deaths and disasters - but when Ragnarok comes he finally pulls it together and reaches some semblance of being happy with who he is. And then Thanos kills him.
