What you just explained goes against everything Star Wars is. Being that said, the prequels also did that with The Phantom Menace when they introduced the Midichlorians.
In any case, the Skywalkers are powerful but they are not the only ones that can use it. There were over a thousand generations of Jedi before Anakin was even born.
TROS did to TLJ what TLJ did to TFA. The story was set up in a certain way and along came Rian Johnson and gave it a complete 180.
I do not understand how you can say there's any character development.
-Luke had a huge character regression just by the notion that he could kill Kylo in his sleep because of his fear of him turning. Contrast that against him 30 years prior with a hopeful personality that went the full length to try to bring back his father from the dark side.
-Rey went to Ach-To and left exactly the same without learning nothing aside that "The force isn't the ability to move rocks". Luke said that she didn't reject the dark side but later when Kylo asks her to join him there is no darkness in her. She is perfect. She learns nothing, she can do everything.
-Finn... Even John Boyega came out only a few days ago to say that Disney didn't know what the fuck to do with his character. He was useless. Attached to a filler sequence of a movie alongside a character that eventually starts rambling about how certain people get rich by profiting on war and stepping on others while it's the same universe that has Death Stars that destroy planets in a single stroke thereby killing billions of people. Oh yeah, Rose, so touching.
Kylo is the only one that has some sort of development.
TROS wasn't rushed. It did what it could. Even if they had spent another 2 years writing the story, there was no way they were gonna be able to get out of the corner that they wrote themselves into. TROS was dead on arrival. Trying to right the ship and tell a story at the same time. The Sequel Trilogy is the result of not having a roadmap. A trilogy that it's in conflict with itself.