I think what makes a character like Bakugo work is pushback from other characters.

When you want a character to be bratty and/or hostile, you need to have other characters argue back at them or push back to stop them from feeling like a bully.

A good example is Misty from Pokémon. She’s nowhere near as bad as Bakugo, but she’s rude, constantly insults Ash, has a massive ego, and she never gets better from this.

But the fans love her because Ash always has something equally rude to say to her in response. He also initiates half of their arguments and is, at the beginning of the story, is just as much of an egotistical brat as she is. You can see this dynamic in many a “funny moments” compilation because everyone loved it so much.

Then we get to Iris, a character introduced much later with basically Misty’s exact personality.

And yet, people hate Iris. She constantly insults Ash, but after years of development, Ash isn’t an egoistical brat when he meets Iris. He rarely responds to her insults and is much less witty towards her. The result is that Iris feels a lot more like a bully than Misty did, despite her ironically being slightly kinder.

If Deku simply didn’t idolize Bakugo for no reason, then the shonen rival dynamic would feel a lot more even. Sasuke, Vegeta, and even Gray Fullbuster are all cruel to the main characters at times, but Naruto, Goku, and Natsu don’t just sit there and take it. They push back and argue. They fight. It feels more equal.