Talking about antagonists, just last night, I read in K. M. Weiland's book that she thought when the protagonist and the antagonist more or less have the similar make-ups, on top of being equal or close to equal in power, the stories succeed much more.

She says, "what if I told you the best stories are those that feature protagonists and antagonists who share more in common than not?"

Then she quotes John Truby, "The contrast between hero and opponent is powerful only when both characters have strong similarities. Each then presents a slightly different approach to the same dilemma. and it is in the similarities that crucial and instructive differences become more clear."

She then explains that because of their similarities, such as personality and values, they share the same goal even if they attack it from different angles, which creates the conflict.

I guess we all know this instinctively, but she put it in words that made it clearer for me.