It very neatly describes the way liberals see the world and political struggle.
Lots of people complain about the anti-climatic ending, but really I don't think it could any other way. I'd like to imagine that there's some alternate universe where Kōhei Horikoshi actually believed in something and Deku was actually built up as the anti-All4One he was only hinted as being in the beginning of the story. Where he opposes all the many injustices of the hero world and determines to change their frequently backwards, insular, contradictory society for the better, and forms his own faction antithetical to the League of Villains and when he finally has his showdown with All4One, Harry surpasses by adopting new methods, breaking the rules and embracing change and the progression of history. While All4One clings to an idyllic imagining of the past and the greatest extent of his dreams is to become the self-appointed god of a eternally stagnant Neverland. Deku has embraced the possibility of a shining future and so can overcome the self-imposed limits All4One could never cross, and All4One is ultimately defeated by this.
But that would require a Deku that believed in something. and since Kōhei Horikoshi is a liberal centrist Blairite that doesn't really believe in anything, Deku can't believe in anything. Deku lives in a world drought with conflict and injustice, a stratified class society, horrendous oppression of the heroes with ugly quirks, the absurd charade the hero world puts up to enforce their own self-segregation, a corrupted and bureaucracy-chocked government, rampant racism, so on and so forth. But Deku is little more than a passive observer for most of it, only the racism really bothers him (and then only racism towards quirk people). In fact, when the Meta Liberation Front stands up against the institutionalisation of dangerous quirk holders and even segregation based on quirk, they're depicted as some kind of evil for doing so. For opposing segregation. In the end, the biggest advocate for change is All4One and Deku and friends only ever fight for the preservation and reproduction of the status quo. The very height of Deku's dreams is to join the heroes, a sort of FBI and the ultimate defenders of the hero world status quo. One4All and the League of Villains are the big instigators of change and Deku never quite gets to One4All's level. Deku doesn't even beat One4All, One4All accidentally kills himself because he violated some obscure technicality where his own arrogance causes him to rewind himself out of existence.
And this is really the struggle of liberals, they live in a world fraught with conflict, but aren't particularly bothered by any of it except those that threaten the multicultural pluralism. They see change, and the force behind that change, as a wholly negative phenomenon. Even then, they can only act within the legal and ideological framework of their society. So for instance, instead of organizing Insurrectionary and disruptive activity against Trump and the far-right, all they can do is bang their drum about what a racist bigot he is and hope they can catch him violating some technicality that will allow them to have him impeached or at least destroy his political clout. It won't work, it will never work, but that is the limit of liberalism just as it was the limit of My Hero Academia.
The whole basis of the ending is hero society needing to operate on a basis of solidarity and empathy. The closing monologue is about the central importance of empathy in society and replaces the aspiration of his generation of being "the greatest heroes" (itself a development from his original more narcissistic conception of himself as the greatest hero) with the claim that their fundamental role is to "reach out" to people, an explicit nod to how Deku tried at the end to save Tomura, the secondary villain. It seems like it probably has some connection to when Uraraka tried to save that blood girl even as she too tried to kill her, since Uraraka ends up being sort of the ideological guide post of the series, but I'm not sure if the connection is explicit.
Deku's single-minded desire to help people even when it seems impossible literally is his superpower, in that it's what set him apart from his fellows, but he ends up going through several stages of being misguided in how to pursue this which he corrects as his bullheadedness repeatedly almost kills him, and his basic conception of the world and society is changed most acutely by a lecture from Uraraka that makes him realize that his chosen one shtick is nonsense.
Yeah which is a nice lesson that empathy includes caring for yourself as well, because your friends care about you and by neglecting yourself, you end up hurting them. That you trust your friends and work together with them.
But it doesn't really address what is to be done in order to prevent the same event from playing again over and over. Which is fine not every story has to be super complicated, still it's disappointing that the best they can come up with is that the Heroes effort will eventually trickle down and end up inspiring others to do better and eventually tech will get so good you won't even need heroes because you'll have police with their metal gears roaming the streets presumably, keeping everyone safe.
While it doesn't provide a roadmap or explain it as much as we might like, the manga is pretty heavy-handed with explaining that a large part of the direct social basis for that kind of behavior was the effect of All Might, Mr. "Everything will be okay, because I am here!" aka the "Symbol of Peace," the man upon whom the entire public confidence rested. The central issue of the narrative in the broadest sense is that the Symbol of Peace was not a great means of social stability and was more a tool for cultivating misbegotten social confidence based on literally lying to the public, which then produced imitators who were liable to get themselves killed like Deku almost did, along with lacking proper solidarity. Though All Might survives to the end of the manga, he explicitly narrates that "The Symbol is dead" and that his paradigm has been replaced by that of the new generation and a more cooperative and mutual attitude toward protecting the population. This is part of the narrative reason that One for All is torn apart over the course of the final struggle and just dissolves, because All Might has positive aspects of his legacy that he passed on, but the singularity of his person as the Symbol of Peace has been surpassed with this new cooperative attitude rather than passed on to some new Great Man. There will never be another All Might, and that's a good thing.