He's...allowed to have his opinion.
But, anyways. Smash 4 is faster and contains more characters. Also can be actively balanced, unlike Brawl. I also believed it's more balanced, and is slightly more technical and more indepth.
Really though, he's entitled to his opinion. If he likes Brawl that much, I can't blame him. Honestly I like Brawl more simply for Sub-space, but that's just me. I do believe Smash 4 is a better game when it comes to the competitive play, but that's also my opinion. It's just like melee guys liking melee more than Smash 4, even if some may find 4 superior.
Also, welcome to the board. Noticed you're new.