Yeah, she is on the edge of becoming a villain but it is more comparable to Mystique in DOFP who turns down killing Trask and does not go down a dark path.
I think using the title “Dark Phoenix” hurt the film in a few ways. I’ve seen plenty people criticize it for not having Jean become full on evil, not realizing that was the point of the story.
The filmmakers consider them prequels.There were no prequels after Days of Future Past; just sequels.