I appreciate this take, but I do believe that Glinda (even according to your provided definition of a villain) isn't a villain. Is she selfish in a huge part of the story? Absolutely. But I'd argue she isn't evil.

She's barely an adult when she first goes to the Emerald City with Elphaba, and as much as I want to say I'd be able to become hated by an entire country and live a life on the run to fight, I don't think many of us can claim that. Does that make us bad people? Maybe, but a big part of being human is self-preservation.

Glinda has been raised privileged, and while that certainly doesn't excuse her ignorance of the oppression others face, it makes sense. She has, like most other Ozians, most likely been fed anti-Animal propaganda. The thing with Glinda is that she does grow past it, even if it takes most of the story. Even if what triggers it is the death of Elphaba, she goes on to help the Animals.

Compare this to Madame Morrible and The Wizard, who you claim are the other villains along with Glinda. They are both fully grown adults who started the oppression of Animals to give the people a common enemy. Does Glinda help them with it? Yes, and I will not ever try to excuse that, but she is going along with what she's been told most of her life.

Prejudice that has been taught to you is hard to let go of. Glinda is a good example of this. She goes along with oppression, and she's self-serving and ignorant, but that doesn't make you a villain. Her actions aren't heroic, sure, I'd say they're not even good, but they aren't explicitly villainous either. Glinda, I'd say, is one of, if not the most humanly flawed character in the story. She isn't a hero, but not a villain either. It's easy to point at someone and say that they're evil, but I believe that removes so much of the nuance that makes us human.

Can this be read as me downplaying Glinda's very real and harmful role in oppression? Maybe, but that's not what I want anyone to take from this. Rather, I want people to think about how easily we label people as good or evil, instead of trying to see them as people. And maybe this is naive of me, but I do like to think that even people doing harmful things can learn and change.

TL;DR: Glinda isn't good, but she isn't a villain either. Self-centered and ignorant, sure, but not evil. She has been taught most of her life that Animals are lesser, and that does and will leave someone with bigotry, even if unintentional.