I think what annoys me most about the ‘Hermione deserves better than Ron’ argument (aside from the obvious and blatant vilification of Ron, of course) is the fact that it completely disregards Hermione’s right to choose.
Hermione chose to start a relationship with Ron. She chose to date him, she chose to marry him, and she chose to have kids with him. She may not have chosen to fall in love with him, but she definitely chose everything that happened after.
By saying ‘she deserves better’ you’re implying that she made the wrong choice. That she doesn’t know what’s best for her. She doesn’t know what she wants. (Alternatively, you could just be saying you don’t really care for her choice, which is- well.) And aside from being just a tad misogynistic, it also takes her character’s agency away.
TL;DR Hermione doesn’t deserve ‘better’ than Ron. You know what Hermione does deserve? She deserves the right to choose. And she chose Ron.