I was asked my thoughts on this by @krixwell-liveblogs, and it got long enough that I decided to just make a post about it.
It’s a fair criticism, but I find the story is more about Midoriya’s spirit, the qualities that made All Might CHOOSE him. It shows All Might’s priorities in choosing a successor; he’s willing to resign himself to finding a philosophically good enough person with a quirk to take his power, but the moment he finds a philosophically perfect person who hasn’t got any powers of his own he drops all his plans and goes with him instead. As a result, the story isn’t some broad parable about how anyone can be a hero, it’s an examination of the kind of person the local Superman equivalent values–kind, hard-working, unwilling to flinch from danger when others are in trouble. Heroic, basically. And he finds that not among the superpowered populace, but amongst the powerless minority that society so often kicks aside, neglects, and generally treats as an embarrassing sideshow.
The whole comic, in fact, has a theme, and it’s not “anyone can be a hero”–it’s “heroes need to be heroic.” Stain’s a lunatic, but he’s a lunatic with a good point who just takes it too far–and his point is that people are getting into heroism because it’s now just another job, not because they actually want to help anyone. It keeps coming back to that point, in fact; the Vigilantes side-story has unsanctioned heroism versus government-sanctioned nine-to-fivers as its central philosophical conflict, and actually itself examines a quirkless hero in the course of things.
This is not to say that people are inherently bad for getting into saving people because it pays the bills; in fact, people like Ochako are explicitly called out as being good people despite their simplistic, relatively self-serving motivations, but while the hero industry in the present day of MHA Japan still largely self-selects for Good People, alarming anomalies like Endeavor are popping up at an increasing rate. Like the American police system, people are starting to enter a job meant to protect people because they instead want to have power–power over the weak, over history, or just in the eyes of the public. One of my favorite bits of subtle character development is how utterly horrified Bakugou is by Endeavor after he learns Todoroki’s backstory; he verrrryyyyy slowly starts becoming more like Midoriya and All Might, though he still has a long way to go. One of my dream scenarios is Bakugou getting to spend time with Endeavor until he loses his shit and attacks the bastard.
If you want a similar story about a powerless hero who stays powerless, I’d recommend the very fun webcomic PS238–though that one’s about an elementary school for the kids of that universe’s supers. I haven’t kept up with it recently, but I enjoyed it immensely.