Of all the changes they made, I feel like one stood out as being the most subtly ingenious - setting up Gaston as an outsider to the town like Belle was, but in a vastly different way.
First off, paying close attention, it becomes clear that Gaston views the town much like Belle does. When he says that it’s “simple”, he means it. And he strides in literally above everyone else on his horse, looking down on them. Gaston realizes that the townspeople are simple minded and that the town is provincial. While they bully and scorn Belle, he doesn’t (at least not in the same fashion or for the same reasons). You could argue that he only doesn’t mock her because he’s trying to gain her favor, but there is no indication that he would have ever had a problem with her reading or teaching other girls to read. He even fakes interest in her books instead of reprimanding her for her “funny” hobbies; he may have looked at this interest in a patronizing way, but it didn’t seem to personally offend him (like his cartoon counterpart who directly states that she shouldn’t be reading books).
He also didn’t seem the type to get upset at Belle or any other woman finding a more convenient way to do chores. And when LeFou tells him the town is bullying her because of this, he doesn’t seem surprised at all by their behavior, almost as if he expected it. We also see hints of his being removed from the town when he tries to “comfort” Belle about the headmaster - I think he’s being truthful here when he says he wasn’t liked either. And, again, he outright tells Belle that their town is simple and that this is all they can expect.
It’s also telling that he finds Belle “outrageously attractive”; some may interpret this as him merely wanting a conquest (which it partly is, no doubt), but I think he also is genuinely attracted to her uniqueness - he finds her argumentative and independent personality appealing, which would seem to imply some sort of free thinking and cleverness on his own part. In some weird, perhaps essentially inaccurate way, Gaston sees him and Belle as sort of kindred spirits - both too good for this town and this life, the “best” that belong together.
Let me digress a bit because now the question comes up as to why he stays in town and doesn’t seek his own “adventure in the great wide somewhere” (which, perhaps, his hunting is a substitute for). I think the answer to this is pretty clear - he’s found a small safe haven where he can get the admiration his low self-esteem obviously needs so that he can keep functioning at basic human levels. Due to sexism, Gaston’s outsiderness is treated very differently by the townspeople than Belle’s. Belle and Gaston are both detached and removed from the general masses, but whereas Belle is ostracized and side-eyed, Gaston is put on a pedestal and idolized (just compare the songs “Belle” and “Gaston”). Logically, this may have something to do with his very real accomplishments as a captain, but it’s also very much rooted in gender roles (Belle has stepped outside hers, while Gaston has not). But if Gaston were to leave, would he find himself being treated as special in larger cities? Probably not. And we see what can happen when Gaston’s self-value plummets - a screw pops loose in his head and he begins literally rampaging, hurting innocent people all in an effort to avoid facing reality.
Back to the main point - one effect of making Gaston seemingly just as aware of the town’s flaws is that it sets him up as much more intelligent than the cartoon. He stays in this town because he’s worshiped, but you can tell he’s looking down his nose at them the whole time, encapsulated by his treatment of the fawning girls. This aligns with this new incarnation’s cleverness. Unlike the cartoon, this Gaston is not dumb. Belle calls him “brainless” because he’s not well-read, but he is in no way dumb. He’s probably not illiterate (he went to school, and he does quote Shakespeare), and he’s more than proficient at gaslighting and manipulating people to do what he wants. He’s also a clever strategist and soldier.
So what does this all mean in terms of character? Why make Gaston as aware of the town’s narrow-minded provincial nature as Belle? Why make him smarter? Well, this has multiple added effects.
1) It means he’s good at evaluating people - he reads and plays the people in the town easily, which makes the ending mob scene much more believable. He rallies these people not just because they admire him (arguably less than the cartoon town did), but because he knows what they want to hear and can play on their narrow minded prejudices (it’s interesting to wonder if he even believed any of the things he was saying about the beast himself). It also means that he may be fully aware of LeFou’s affections for him, and was choosing to ignore it and/or use it when necessary.
2) It also means that his failure to acknowledge Belle’s feelings about marrying him are not due to obliviousness or stupidity; he is willfully deluding himself into thinking he has a chance. This adds an element of instability to him that becomes more and more dangerous as the movie progresses (just watch his reaction to Belle closing the door on his face - that’s some hardcore reality avoidance). Gaston’s sanity and self-worth is holding on by the thread he’s created in his own mind that he’ll win Belle.
3) It makes him scarier as well. Cartoon Gaston was scary because he was big. This Gaston is scary because you can see him evaluating, judging, and plotting. You can see him using his looks to get what he wants and, unlike the cartoon, affecting a sort of tender sincerity to deflect suspicion. His ability to be metaphorically outside looking in at this village makes him capable of manipulating everyone, except Maurice (and you can see how Gaston handles that)
4) It humanizes him too. One can’t help but wonder what he would have been like without that fatal need to be liked and admired and with some sort of societal boundaries to keep his ego and entitlement in check. Or if he had simply taken Belle’s rejection as the lesson in humility it should have been and used it to evaluate himself and his qualities, instead of letting it destroy him so much that his behavior devolves into irrationality and outright cruelty, even towards those that he seemed to care about at least a little at first (LeFou and even Belle). In fact, his transformation is a mirror reverse of the Beast’s - Gaston transforms into a monster as the movie goes on, while the Beast becomes more humanized. Both the beast and Gaston are subjected to a lesson in humility, and react in very different ways.
Overall, I think if Disney had simply recreated the cartoon version of Gaston, he would have been a laughingstock - a character that seemed too unrealistic and static. But by rounding him out, he becomes dynamic and I think he’ll probably live on in this version as one of the best Disney characters (not just villains) of all time.