Matchmaking does not match people based on skill, at least not in Destiny. The only mode that has selective matchmaking is ToO and that is only based on connection quality. I would hardly call playing on your brother's account once, or even occasionally, evidence that the players on PS4 are worse. Even with my mediocre skills I dominate in some matches, but then there's other times where I'm up against a premade fireteam full of tryhards, or some MLG pro equivalent and I stand no chance.