How are match ups determined?

I was just wondering the logic behind match ups in normal Draft Pick. I know no one thinks normals matters but when i want to have fun with my friends that's what we play. I have heard that if you queue with a pre-made it gives you a harder match up. with that in mind we never get in games that are even close and you can say rank does not mater in normals but higher tier are obviously more skilled at the game. The last example was My Team ( No Rank Lvl 27, Silver 2, Plant 5, Gold 2, Bronze 1) Bronze 1 and silver 2 are the premade (technically silver elo but bronze this year not that it should matter that much).. their team (Diamond 5, Gold 3, Gold 2, Plat 3, Silver 2) Now in what world is that even close to being fair??? ohh and the Diamond 5, Gold 3, Gold 2 was a premade. I understand it would make the queue last a lot longer to get perfect matchups but this is not even close to being fair and completely ruins the fun and almost all of our matches end up being like this.