I agree with you on all of this except the point on Bumi. I think the change to his character is great and makes him feel more realistic! It felt like the live action Bumi was trying to be as fun loving as animation Bumi but can't hide how deeply the war has changed him for the worst, which makes sense since he is probably the only one (or only handful of people) to have lived and fought through a hundred years of war. He's also trying to be a good friend to Aang but can't help but feel resentful towards him for abandoning his role as the avatar.