Can someone explain how ranked matches you up?

So I don’t play very many of the ranked playlists. I usually get maybe halfway through being ranked on each game mode each season. Today I decided to play some SWAT. I am not ranked in SWAT currently and have hit platinum (5 I think), but never broken into diamond. So the first game I played today, my team consisted of me, anther unranked player, a gold and a platinum; the other team (mind you they only had 3 people for some reason) consisted of all diamonds. So either the few games I’ve played it’s projecting me to be put in diamond (which it’s not), or the ranked playlists are just whack.

I believe you should have posted here MATCHMAKING FEEDBACK & DISCUSSION