Umbridge is probably the most hated villain in all of the HP fandom if I had to hazard a guess. Even worse than someone like Bellatrix who was pure evil and took out a really beloved character.
Rowling is phenomenal at creating every variant and shade of grey in her characters from the willfully neglectful to the truly maleficent. Even the way pretty good characters like Harry’s friends (except for Hermione) will get jealous and turn on him at times when things look bad for him. People exploit others, turn a blind eye to injustice and cruelties and chicken out when their neck is on the line.
Snape gets remembered as a hero but he spent his entire adult life avenging childhood slights and picking on children. He torments Nevill and does everything he can to make Harry’s life miserable if he can. Draco is seen by many as redeemed because he doesn’t choose to destroy every enemy, including Harry at one point, but as Rowling has pointed out -he’s still a horrible racist and it’s only because his wife doesn’t believe in his “mud blood” views that his child is raised differently.
Rowling gives a few female characters some near saintly personalities like Hermione and Lily, but pretty much everyone else is a very complicated, mixed bag of personality traits and frailties.