I guess it depends on what you’re talking about specifically but I could not disagree more, and I can’t think of a single MHA villain aside from Tomura who has this mindset. Even AFO isn’t nihilistic, he has a very specific vision of the world he is trying to create.
Tomura has this very specific understanding of society, but most of the villains, or at least the ones who gain praise, are "we live in a society" type villains.
The existence of the MLA and their ideals is a pretty targeted and specific criticism of society that extends beyond just “destroy the whole thing” (that is Tomura’s job).
The thing is the meta liberation armies ideals are not a monolith. Shigaraki does not have any long term goals beyond "destroying everyhing", but the rest of the MLA, especially the remnants of the PLF, have a very specific vision for society. Namely a kratocratic society where position in society is determined by the usefulness of ones quirk. This is evidenced by guys like Geten and Trumpet, who both have an emphasis on the society they want to create being one that values the type of quirk an individual possesses.
MHA has also made plenty of criticisms about how no hero aside from All Might really fit the definition of being an idealistic hero,
All Might doesn't even meet that standard, and is actively criticized in the story for his role in contributing to the current situation.(admittedly, this is recuperated by Stain, but Stain is a fucking crazy murderer)
as the other heroes either possesses secret cruelty (Endeavor), were image obsessed (Mt. Lady and co.), did not care about saving villains so much as simply stopping them (Hawks),
Endeavour is right, but the funny thing is that as soon as All Might left the scene, heroes like Mt Lady who were initially obsessed with image actually began to change for the better to become true heroes. Hell, that was also true for Endeavour himself, who is beginning the journey of trying to atone for his past deeds.
Also, your just blatantly wrong about Hawks. Yes, Hawks did end up killing Twice and regrets being unable to save him, but he actually did try to "save" Twice to begin with. His initial efforts were mainly centered around trying to help Twice rehabilitate, not just stop him like your suggesting.
If you think Tomura is generic, I’d ask you which other Shonen villains resemble him as a character as he is very much a one-of-a-kind villain in this genre and in this manga lol.
Eh, he is a villain that is cut from the same sort of cloth as tons of other villains(Doflamingo is a character with the same sort of endgame, and also possessing in a tragic pathos filled past, even though they are distinctly different in other areas, they actually do have similar character beats in their backstory, even have the freaking "groomed from a young age to be the pinnacle of evil"). I wouldn't exactly say he is generic, as much as he is painfully dry, uncharismatic, and totally lacking in chemistry with any character he interacts with. Its that total lack of chemistry that allows someone incredibly generic like AFO to be a better antagonising force in the story.
But if by generic you mean “one-note”, as in “all he wants is destruction..” well yeah, he’s supposed to be the opposite to Deku who only wants to save everyone. Deku and Tomura represent the purest hero and villain ideals respectively.
The only villain I've called generic is AFO, and he is by far, the best antagonist force in the manga by a gigantic margin.
Shigaraki is not really the opposite of Deku though. I know people like to say he is, but he is similar to Deku in key area's, and that is reflected in his relationships with other characters. Both Shigaraki and Deku highly value their comrades. That is a major point of similiarity that makes comparisons slightly redundant. Shigaraki is not a pure villain by any metric.
AFO actually does a better job of "inverting" Deku's values than Shigaraki. AFO is a perfect inversion of the concept of heroism. He is a smiling, maniacal, petty villain, who uses his comrades and subordinates to his own ends, all for the sake of pursuing personal power. Even AFO's name is a total inversion of Deku's power of OFA.
He also has developed a better relationship with Deku than Shigaraki. While Shigaraki just has zero chemistry with Deku as a person, AFO actually is a good villain because he is someone perfectly understands who Deku is, and views the character traits that convinced All Might that Deku was worthy of OFA as "useless". There is an actual clash of values there which facilitates there to be real interpersonal conflict between AFO and Deku, something that does not exist between Deku and Shigaraki.
So in summary, AFO, the most generic evil overlord shonen villain in MHA, is a better villain than Shigaraki, and does the shit that Shigaraki is supposed to do as a villain better than Shigaraki. AFO as a villain is just a better foil for Deku than Shigaraki, who is just kind of shit.
I'd also say that Gentle was a better foil as an antagonist for Deku than Shigaraki, and that guy was fucking youtuber.