I think was something that had been previously explored in books with other Jedi and since Luke had been off collecting old Jedi manuscripts it isn't outside the realm of possibility that he taught himself how. And given that he was the son of the "chosen one" it wouldn't be a stretch for him to be a powerful Jedi himself. The bigger problem I have was Finn and Rey being poorly developed like they were teenagers. The X-Men franchise does a better job developing actual teenage mutants than the current Star Wars people have developed Rey's character. That's why I said Dave Filoni needs to be more involved.
When Filoni was working on The Clone Wars series, Lucas was present at every writing session and would explain various parts of the Star Wars universe. Filoni has shown he can create a new character and keep them true to the original visions Lucas had. If they revive the Obi Wan project then Filoni needs to be the one who writes it otherwise it will be crap.
So...Luke finally became as powerful as Dr. Venture's former tenant Dr. Orpheus? That's disappointing. I regretfully watched The Force Awakens and have not watched another Star Wars movie since. That saddens me greatly given how much of my life I've spent loving the original trilogy