I would say that Mineta fits more into the "normal" sphere of how male perverts are usually portrayed for comedic relief in entertainment media than in real life on a constant basis. Groping a female classmate's cleavage or posterior, manipulating the girls in your class to wear revealing cheerleader dresses for a sports event, looking through a peephole to see the girls changing in the locker room, and trying to sneak over the walls to see the girls bathing are all things I have seen in other shows, movies, and video games for comedic relief moments. I've even seen episodes based entirely around covert female underwear raids in Spongebob and Codename: Kids Next Door.
This isn't to say that just because these things often happen in media then it's okay to continue using these scenarios for comedy. At least 8/10 times it's always at least slightly disturbing and promotes a false idea that this is how boys usually/should act and the punishments usually being either a slap on the wrist, while making justified female outrage reactions seem overblown or funny instead of being given the weight and respect they deserve.
I can believe that some guys could talk about imagining these things and even might try doing once or twice of these things during their lives. But again, only some guys, and only a couple times unless the environment is really messed up with seriously negligent faculty.
Horikoshi is 99% confirmed to be a bit of a pervert, although I'd like to think he never attempted any of these things and just really likes both these kinds of fantasies and seeing these pervy scenarios in other media (and in shonen manga, there is no obviously short abundance for them. Just look at Master Roshi in Dragon Ball). Which is… well, I'll let you judge that on your own. Although I would also add that a small part of Horikoshi's intent is to show the less pure reasons people seek Pro-Hero status, which is similar to the commercialization aspect in Yaoyorozu's "field training" and Endeavor's abusive methods in becoming the best Pro-Hero no matter what.
Characters like Mineta are a symptom of the cultural stereotype that all men are bound to be horn dogs, which definitely exists. A stereotype that some people like to claim is true either out of ignorant bias or to self-project. It has some basis in reality given how often and how big sexual harassment can be, but it tends to get overblown to ridiculous acts and embodying the whole male gender with only slaps on the wrists in entertainment media, though that has thankfully been changing very gradually. I think that stereotype itself even feeds into how people of either gender come to think sexual harassment is okay to allow and enact.
Further, I think the main problems with Mineta can be summed up in two ways. One is obviously how over-the-top his perverted antics are when that should not be allowed in a school setting. Or any setting for that matter unless he were a villain with a negative portrayal.
And two is the sheer frequency of Mineta's perverted antics. By that, I mean how his character is COMPLETELY DEFINED BY IT. Usually pervert characters get one or two other big traits and story roles aside from just leering and sexual harassment.
Master Roshi is a martial arts expert that helps Goku and Krillin train to learn new techniques. Sanji is a chef who is absurdly prideful about his cooking and will never hit a woman because of asinine chivalry. Brook is a musician who loves making skeleton puns, is an ironically rude gentleman, and believes that life should never be taken for granted. Brock in the Pokemon anime (one of the only perverts that I find tolerable who actually knows proper boundaries and doesn't have disgusting intentions) is a former gym leader, is knowledgable about Pokemon breeding and aspires to become a doctor. Kaminari, a supporting character in the very same series as Mineta, is Jirou's comedic/supportive best friend and frequently short circuits into being a brain-dead idiot.
Even though those kinds of characters can do the most insufferable perverted antics ever, they have other personality traits and plot relevance to bounce off of in-between their pervert stints.
But Mineta is JUST a pervert. He hardly does anything that isn't related to that. I'm sure that sexual harassers and even rapists in real life actually have other hobbies and skills they like to enact in than just thinking about and having sex. Not that those traits redeem them in the slightest, but even the worst kinds of people usually have some depth to them than only obsessing over basic primal instincts.
Which is a shame because during the rare instances when Mineta is NOT acting like a pervert… he's actually kind of funny. Which I know sounds bizarre, but it happens once in a while during moments like this:
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An insecure Mineta with the occasional superiority complex is much more hilarious and interesting than future sex offender Mineta. But shonen's gonna shonen. Which means Horikoshi's gonna Horikoshi. Amounting to how Mineta's gonna Mineta for at least the rest of the main cast's first year in high school unless character development shockingly happens.
…Looking back, I can't believe I actually put effort into writing that much about a garbage character like Mineta.