Ok. Since you are proceeding from this definition, I will use it in the current answer, too, to avoid ambiguity.
Yes, sure. They are not necessarily heroic themselves, despite they often save people's lives (which counts as a heroic thing).
I don't know much about T'challa, so can't talk about this particular character.
Take into account, that I've watched Marvel/DC movies and cartoons more, than read comics (but I read some of them, too). And I didn't see any moral dilemmas in movies about Superman, Spiderman, CatWoman and others. Also, from what I've seen about popular heroes, they more often face trauma because of villain's deed (like Batman) or random bad events, not because of things, they see and do at their "superhero work".
Yes, it is a metaphor for moral purity. And I think, that classical heroes really think about themselves as a moral pure people. Even if they make "mistakes" (often ridiculously insignificant), they always repent and their nimbus quickly starts to shine again. If they face trauma, it doesn't make them insensitive or cynical - instead it fill their hearts with even more desire to fight evil. From what I've seen, they don't really plunge too deep into dirt, not in that degree which would really shake their ideals. Even if they tread in a puddle, they quickly put mud away and continue think about themselves as a "totally good guys".
Yes, it is not about hero vs. antihero discourse. Just about how simple and not-pathos heroism is in reality, and, in the same time, with a such a high price it goes.
No. I never wanted characters to be saved by superpowers or Deus Ex Machina. Such a things always have a taste of lies, I don't believe in them and don't feel any good, when I see it. (In the same time, I'm satisfied if characters overcome obstacles with their cunning, cleverness, willpower, special skills etc; not because of miracles).
And what I want to say is, the fact itself, that superheroes don't pay price, comparable to price of real-life heroism, makes their heroism cheap.
Yes, they are. And there is their main problem, in my opinion. Honestly, I don't understand, how clever adult people can enjoy such a things and empathise to such an unrealistic, cardboard "people". I can't believe in superheroes even for a second, so watching or reading about them don't give me any therapeutic effect, just the opposite.
As I've already said:
If the author don't want to reveal dark topics... what about not even starting the topic of "whom choose to save, and who will die", instead of giving stupid, unrealistic answer to it?
Well, from what I know, "real heroes" certainly lose idealism at some point, and their moral also often changes after everything they went through.