MATCH MAKING IN LEAGUE

So I just played a normal game with a friend ( cuz the game is tilting and toxic without one) and I had a PLAT 5 jhin in my team. And everyone else including the enemy team is silver. How is this fair? Why is a PLAT 4 jhin main on my team? My team won because of course the jhin destroyed the bot lane and snowball the entire game. But is that fair at all?