Depends on your definition of "real".

I think that's part of what you're asking; for each person to define that in their answer, but you can't get an answer without the terms in the question being defined.

Also, who is to say there isn't more than one "real" villain in each game? Yevon, Seymour and Sin were all real villains in the sense that they all were the party's antagonists and presented conflicts in the story. Same with VII.