Find out how fast he wants to be. If he's too stubborn to learn a new method because he thinks his is faster, the only way to prove that is to show him videos of people using methods other than LBL that are fast. In his defense, I can sub60 the Rubik's booklet way of solving a cube, and in some people's eyes, that's fast. Not everybody wants to Sune OLL til it's solved then do a couple PLLs. I had friends like this, but they only wanted to be able to solve it and didn't care about speed. I'm sticking to my original words though, ask him how fast he wants to be and show him how LBL does have it's cap (although sub20 with LBL + 4LLL is quite an achievement, it's still incredibly difficult to achieve. sub20 with CFOP is quite a bit easier to achieve).