TLJ is definitely not a well written movie. Not by far.
And this is not about Luke, it's simply about keeping a coherent tone within the movie, not to mention within the series of movies, about staying within the boundaries of logic set up before, about understanding the underlying themes.
As for better acting... well, other than Hamill, I didn't see much to write home about... Fisher was particularly bad IMHO, and while Boyega and Isaac are fine actors, their poorly written roles didn't really help their cause.
It seems to me people just assume the acting and writing must be better, when it's actually not. The dialogue may flow more, but that doesn't mean it's a well written movie.