i think some examples of good villain Ones are the ones who are doing what they think is right. But, they are often misguided by their own ideals that they often don't see the issues they are causing, or care to address those issues. _SPOILERS IF YOU HAVEV'T SEEN IT _ For example, Amon, from legends of korra, was an activist who wanted to speak out against the benders because of the group of bender who were abusing their power to hurt people. The idea was to remove the powers of the benders so that they are like the normies, and cannot use that power again. But, as the story progresses, Amon then uses his power against those whom he sees as unfit by his standards. this feeling of power in the followers, and the training in anti-bending fighting style caused the followers to become more aggressive, and eventually leading to a war with the police, and they capture indiscriminately. This cause originally started for good, but the vision became twisted, as there 'oppressors' became more active because of the twisted evil doings of the group. I also apricate that in that arc the the villian was humanized, where you learn the Amon is a bender himself, and grew to hate himself, because of his poor father in his childhood. so he wanted to remove al bending.
So i think having a balance of humanization and motive helps. why does the evil overloard do what they are doing? why do they want it, and how far will they go? Idk if you should regress the dredge, as their role in the story becomes that of a savage animal. For me, that is ok for plot, but i think if you do do that, maybe some of them turn, and not all. I think you could have a really interesting dynamic, where the readers learn about the dredge how they feel about their history. perhaps you can find villian not in people, but the perception of people.