TFA does go out of its way to make Rey’s victory over Kylo make internal sense, but that doesn’t mean it was a good story decision. Really, other than showing off how powerful Rey was, and bruising Kylo’s ego, it doesn’t accomplish much or advance the story. Rey defeating Kylo doesn’t have any significant effects on the plot, since Rey and Kylo are separated by a crevice and both escape SKB regardless. The fight being a draw would have had the same story result, with Kylo still being impressed by Rey’s power.

Generally, it’s a bad idea to so thoroughly humiliate your villain in the first part of your trilogy, especially if there are plans to kill off his superior and make him the big bad in the future. Watching Kylo flop around in the snow took away whatever degree of intimidation he had left, and made his character in need of rehabilitation over the following films. TFA implied this would happen with Snoke ordering that Kylo be brought to him because “It is time to complete his training.”

TLJ never gives us that training, though. Instead, it lampshades how embarrassing Kylo’s failure was, which was a good idea, but the movie never tries to rehabilitate Kylo or make him a viable threat again, even after Snoke’s death. So, the movie ends with a weak main villain leading into Episode IX. Given that, it’s no surprise at all that TRoS brought in Palpatine, and that Trevorrow’s DotF script tried so frantically to buff Kylo and make him a worthy enemy.

Also, of course, Rey being so powerful already undercuts her need for training. And her line to Luke about how she needs to bring the Jedi back “because Kylo Ren is strong in the Dark Side of the Force” rings hollow given what we know.