Well my statement wasn't to say literally all shonen is bad. That would be silly. Battle shonen tends to be pretty mediocre, in my view. The cast, especially the female leads, tend to get treated terribly aside from being generally poorly written, and the endings never seem to be very satisfying, because they're written in a way to just keep on going rather than having a clearly defined start/middle/end. That's not to say you can't enjoy them either, there is plenty of shows I've enjoyed. Hell, I've read through all of Bleach, Naruto, Fairy Tail... and for the most part, enjoyed them (Bleach is really quite bad though, was mostly hate reading by the end).
The problem is, and this applies to many fields so it's not a unique issue, these series tend to be what get latched onto and hyped up. And that's the objection we're taking.