I agree, I thought that they probably should have just ended the movie with Rey, Chewbacca, and R2 blasting off into space. If they needed Luke, perhaps just his voiceover of "The Force is strong in my family."

I think that Kylo Ren's lightsaber skills match well with his character. He's shown multiple times flailing about with his saber trashing computers and the like. It's like a whiny brat with a toy. He doesn't truly understand it, just that he's supposed to have one.

I think that he's very much like Obi-wan in this. "I thought I could train him as well as Master Yoda." In both cases their apprentices fall to the Dark Side, and both leave the galaxy to fend for itself while they hide. Granted Obi-wan was looking over Luke, and thus had a purpose, but I assume Luke does too.

Perhaps he needed to go commune with ancient Jedi. Find old teachings in holocrons; speak to the force ghosts of Obi-wan, Yoda, and the like; meditate and learn first. He never had a full teaching himself, so it's hard to go and teach others. At the end of RoTJ he's still just really a padawan, although claims the title of Jedi.