I think a lot of people need to realize that "undoing" an established plot point and "not conforming to my headcanons" are not the same thing.
Like Luke's relationship with Rey. A lot of people on tumblr complained about that when TLJ came out.

Granted, many of them wanted Rey to be his daughter or niece, but whatever.

TFA establishes Rey as someone who worships Luke. She's heard stories, doesn't know if he's real at first, but wants to find him. She thinks he can fill the void that her parents left behind.

But she doesn't speak to him until TLJ. And when she does, it's a "don't meet your heroes, kids" moment. Their relationship is strained throughout the movie, but she respects him by the end.
That's not undoing TFA, that's just continuing a story.

Rey respects him by the end, but note that she stops calling him "Master." And their relationship is tied directly to his relationship w/ Ben-the idea is that he would help Ben in IX too.
But TROS resets their dynamic, framing Rey as meek and insecure, while Luke

is the wise and powerful master.
That in itself is not the biggest problem, it's been awhile. I don't like that she is so insecure around him, but that's just me.
My problem is that when you put that together with the events of TLJ, it becomes a retcon.

TLJ Luke realized the importance of love, compassion, and family and that the Jedi should move beyond their old dogma. That's what the Yoda scene was about. He said "see you around, kid" to Ben. Yet TROS Luke doesn't follow up on that at all.

THAT's undoing the established plot.