7 and 8 do not link together. The characters from 7 are not the characters from 8, because both directors had their own interpretations. When people defend 8, they are defending their love of the movie and their parasocial love of Rian, not its cohesiveness in the trilogy or how well it meshes with the other 2 films.
Rey was someone in TFA, Rian decided she was “no one” and then JJ decided she was someone again. There is no way that Rian thought she was a secret Palpatine when he made 8.
Kylo was Vader obsessed in TFA, 4 minutes later in TLJ (in universe time) he isn’t, and ROS he is back to Vader obsessed.
Snoke was a mysterious new emperor in TFA, TLJ said he was a joke nobody, ROS then said he was back to being a mysterious new emperor (clone thing). This is on record that JJ did not expect Rian to kill off the big bad unceremoniously.
This is not saying JJ’s writing is good. This is saying that the two different directors clearly had different visions of what they wanted the characters to be.