You are right in one thing: most of the accounts in the leaderboard are either fake plats or alts. Thing is, a few of them aren't any of those. In a way, pvp and pve are similar in this fashion. Really good players are way better than any gold or even plat players since (excluding build carry) the learning curve is so high. Also, Doesn't this apply for everyone? I also win more when I am queueing with a friend who is on par with me.