As for the whole thing about Rey defeating Kylo in a lightsaber suel. Aren’t we forgetting that Luke never had any lightsaber sparring training what-so-ever. He learned to block some laser-bolts from a small harmless droid by Obi-Wan, and then he ran around in a swamp with Yoda on his back learning mostly levitation and some Jedi philosophy. Even if you count the novelization or the deleted scenes as canon all the lightsaber training he did with Yoda was cutting a few metal rods throws into the air. I also seem to recall that he didn’t do that well on that test.
Aren’t we kind of judging this film by PT logic? That it’s the moves that count, not the use of the Force. Pre-PT material often put a lot more of a focus on the importance of channeling the Force and fining inner peace and control, which is exactly what Rey did in TFA. A lot of the mystical elements of the lightsaber was lost in the PT, but Kasdan and Abrams seem to have brought it back here.Luke got his ass kicked by Vader. Then he trained for three more years to finally become a Jedi. Where and how he trained nobody knows, but it’s nice to have movies that don’t spoon feed you everything, and allow you to fill in the blanks yourself. The only relevant exposition needed at the start of Jedi was that Luke’s powers had grown immensely since the previous film.
Even then, Luke wasn’t able to defeat Vader until he used the dark side of the force in their last battle.
Luke lost yes, but he still gave Vader a run for his money, even to the point of wounding him slightly. Also, there’s two-ish years between ANH and ESB, in which he only had himself to train with. He had no practical fighting experience until he faced Vader. And there were only a few months that passed between ESB and ROTJ.
The OT was more focused on the Force rather than sparring skills. And yes, Luke only won in ROTJ because he used the Dark Side. But that seems to be what the OT went for, Force skills over dueling moves. Vader and Luke won because they used their aggression to overpower and frighten their opponent, and Rey as well as Obi-Wan (before he let himself get killed) used calmness to channel the Force in order to win/survive.
I haven’t’ actually red the novelization of ANH, but I recall from the comic adaption(s) that it talked about how they channeled the Force through their blades. Even before the ESB fight, Lucas had a pretty decent excuse for the slowness of the fight. It’s more of duel of wills then sword-waving-skills. If Rey managed to find her inner calmness, then purely as a fight of wills and Force strenght it’s really not that weird that she managed to defeat the wounded, angry, emotionally conflicted, and even somewhat frightened, Kylo Ren. And she’s proven that she has some skills with a melee weapon before (e.g. her staff).