I think the idea that game X is bespoke whole game Y is more general relies on a flawed conceit - that the purpose of a roleplaying games rules is only to represent a type of fiction well.
@payn, I think your post rest on what @Campbell called a "flawed conceit", namely, that the job of the RPG is to represent a certain fiction.Well, Mutants and Masterminds can do teen emo sups, but it can also do a variety of other sup stories.
I agree with @Campbell, though:
once you actually look beyond the fiction and look at the differences in gameplay you have phenomenally different games that are structured differently, bring players' attention to different parts of the fiction, reward different sorts of play. In terms of play experience, one is not more bespoke than the other. The actual game part could not be more different.
I can't comment in any detail on this in relation to Masks vs M&M, although what Campbell says seems highly plausible to me given what I know of each game system.The core loops of play, the things the mechanics reinforce, the focus on the characters' sense of identity and their lack of ability to control their emotions/powers will not be as present. Wherein Mutants and Masterminds a lot more focus on the specifics of their powers will be present. The actual experience of playing is going to differ dramatically.
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Because they can exhibit similar fictional spaces does not make them substitutes.
But I can say that what Campbell says is absolutely true of the play of Burning Wheel compared to any version of D&D that I'm familiar with. I have played BW where a debate between two travelling companions about whether or not one will repair the armour of the other matters - in that it is high stakes in play, it can be resolved in a way that is not predetermined and does not just depend on the two players talking it out, and it feeds through to the game's system for recognising and rewarding significant episodes of play. D&D can't emulate this play, even if it permits a game to include the same fiction.