Any given American superhero can have a reasonably well-defined powerset and limitations around which a story can be built. However, the available powersets of any given American superhero are effectively arbitrary, and because they tend to crossover a lot from the looks of it, or even just to have a suitable nemesis, it seems that at any moment we could encounter a new character of any possible kind of power.
The superheroes don’t appear to exist in an ecosystem where repeated layers of competition cause things to be shaped according to the pressures of the environment, like humans or main battle tanks. At any moment, someone might be under the effect of powerful mind control, or a man at the atomic scale could be infiltrating a character’s alien super-kidney, or a character could be revealed to be a giant flying psychic death planet in disguise. The power levels just feel kinda arbitrary.
Remove the crossovers and the powers are more likely to come from the same source or exist within the same framework, and therefore might be governed by something like RPG classes in terms of balancing, tactics, and expectations about the world. However, this risks moving you out of the superhero genre and into one of the fantasy genres or even cyberpunk.
We can also establish expectations about power levels by having a season-long plot with villain progression such that we know this episode’s villain is more powerful than last episode’s villain, and thus might potentially defeat the protagonist.
This isn’t to say that all American superhero stories are limited in this way, but rather that, if someone says that they don’t like American superhero stories and prefer anime, something like this may be one of the underlying reasons.
I mean, maybe, but I suspect that most of the time it has much less to do with any particular issue of plot crunch and much more with issues of theme / aesthetics / psychology / narrative construction. It’s true that American superhero comics are more random with their power level stuff than anime usually is, but this seems like a really minor issue next to the fact that American superhero comics focus a lot less on character and a lot more on plot.
The analogy to Western video RPGs vs. JRPGs feels apt.