It's a very fair question. Stargirl in particular seems like she bridges the gap pretty cleanly, doesn't she? Especially with her whole relationship with Billy -- the consummate henshin hero and pretty manga-like in his own way -- and how that has been playing out through the years, totally seems like a Magical Girl manga's secondary storyline. A lot of it does have to do with presentation, and it's hard to say exactly what that presentation should be.
I have a pretty clear answer for you when it comes to superteams, though: when you look at something like the JLA or JSA, they've got this wide variety of powers and origins, you've got aliens and atomic fusion, higher powers, straightforward training, mystic dimensional genes, chemicals, lycanthropy, etc etc. In general for a Japanese "superteam," though? You don't have that variation of origins. Each member will basically come from one type of power source. Now, each member will use and exhibit those powers in a different way, but in general you're not gonna get "Green Lantern Ring" and "Speed Force" in the same group of comrades. (Although GLC is actually a great example of this sort of team dynamic in western comics, or the X-Men to a certain extent) Of course, this is because western serialized comics come from a rich tradition of inter-universe crossover continuity, whereas each manga and TV series all operates within its own individual heroes that don't have anything to do with others made by the same publisher, but there's some interesting notions one could glean from this attitude of "You can still display individuality even as you conform to the majority," if one were the gleaning type. It also creates competetive drama foil for heroes if every "powered" being in their universe shares the same sort of power; "My Burn Energy is weak! I must train harder so that it will exceed the enormous Burn Energy of Blazago, my dark rival!" and so forth. Although, on about a fifty-fifty basis, the villains of the series might have a power source that's diametrically-opposed to the heroes'; evil aura against his/her noble aura, or whatever. Which is another reason why the GL corner of the DCU has been feeling so much like a manga universe as of late.
Examples of these teams include Yu Yu Hakusho, Saint Seiya, Sailor Moon, Shaman King, etc etc. Note how this trope sort of mutates itself to fit even Pokemon; everyone's "power" is the ability to summon these critters to fight, they all have their own traits and tendencies in a match, and there are clear criteria to indicate if your "power" is more or less than someone else's. Now, there are exceptions and instances of teams composed of the genre-blender that US comics use (Get Backers, off the top of my head), but almost without fail in those instances the teams will function less cohesively and not be as attached to each other. I would say that this alone was one of the foremost reasons that the Super Young Team didn't have any real Japanese superteam flavor to me; the fact that these people all seem to have somewhat-bastardized versions of American superpowers is almost less significant than that they all seem to have gotten them in a different way than each other, with no symmetry between them.