Thanks for making the effort to put together an actual argument. Full disclosure, I find Rey kind of boring as a character, I just cringe hard whenever I see asshats decrying every competent character as a Sue. Let me try to address each of your points.>Well she seems to be an expert user of the force, although has no training, and until the middle of the episode 7 doesn't even know the force exists
Thing is, that's never been how the Force works. We've seen different untrained Force-sensitives channel the Force in different ways before. Young Anakin had unnaturally quick reflexes, Leia was able to mentally speak with Luke, Luke could fly a fighter and hit a bullseye purely by instinct, and Rey can impose her will on the weak-minded. Seems fine to me. As for "expert?" If she responded to every successful use of the Force with nonchalance, then you might have a point there. But she's clearly surprised every time it works. Sues don't get surprised.>and then beats Ren at his own mind powers
They're not "his" powers though. He doesn't even know Rey is Force-sensitive, so why would he go into that interrogation prepared for it? And that aside, the young hero experiencing a surge of raw power right as they awaken their abilities has always been a common fantasy trope.>then beats him in a lightsaber duel still with no training
You mean aside from her skill with melee weapons that's already been established, Ren's crippling stomach wound, and the fact that he's clearly not trying to kill her because he wants to convert her to his side? That's perfectly believable.>Luke should have been focused on, in the extended universe his stories are vastly superior to the story in the new movies.
I think focusing on Luke more than they did would have undermined TLJ's theme of passing the torch, but I'll grant that this is a much more subjective point. EU was a fucking shitshow though, they were right to drop it as quickly as they did.