He's darker and edgier, not an asshole or an idiot. He works with the Doctor because the Doctor is an important part to his future and could ruin him if pissed off. And when Doc does overstep, Edgezuku DOES put him in his place with coercion and intimidation. But he can't go around doing it all the time or the Doc wouldn't help him find the people who hurt Inko and put them down like the dogs they are.
As for the love interests, he has no reason to bully them. For one, he likes them. For two, he needs them to power his quirk. So being an asshole would be counterproductive and stupid.
Finally, as far as the teachers go, well, they're his teachers. They're kinda important as far as graduation goes, and Edgezuku would still very much like to graduate from the most prestigious high school in Japan because obviously. So some amount of sucking up is required regardless.
There's a reason moral behavior is considered such. Pro-social behavior isn't just healthy and nice, it's unironically a more effective means of getting your way than anti-social behavior.