My personal experience is that the former reliably preserve a "superhero"-type experience, that actually feels like the comics, movies and so on. The very best-designed (albeit highly-specific) superhero RPG I've ever seen, MASKS, is clearly this type.
Whereas the latter is always, always living near the edge of 'descending' into being The Boys! And the more "simulationist" it is, the inherently closer it is to that edge!
Some it's a few feet from the edge, because literally all the players are very studiously making their superheroes act heroically, and the GM is doing the same with the villains, making sure that Badguy Hulk Expy doesn't just one-shot incompetently played Batman Expy, even though he easily could, and so on, and maybe the system has some kind of narrative tokens or the like to help with that. But sometimes they're absolutely teetering on that edge (esp. with say, GURPS Supers or the like), or just straight up falling over it directly into The Boys-land.
And maybe The Boys-land is where you want to live! But I feel like that's not actually a "superhero" setting, that's a sort of "gods and monsters" deal that deconstructs (and does not reconstruct) superhero comics as part of its aesthetic.
(I shouldn't exclude the middle too much here - like, M&M is pretty firmly in the middle imho, at least last I looked at it.)