Since we’re talking about disappointing aspects of the sequel trilogy, I’d say one of the most disappointing aspects of the trilogy is having The Force Awakens and The Last Jedi take place so close to each other.
They could’ve had The Last Jedi take place two or three years after The Force Awakens, with Rey training under Luke since after The Force Awakens. The Resistance subplot can start off the same (the whole evacuation and space chase stuff), Kylo has continued his training that was mentioned by Snoke in the last film, Rey and Kylo have their interactions, etc.
These are just random ideas I’m throwing out there.