Matchmaking-System broken?

Can someone tell me why matchmaking in this game is so messed up, especially in 3v3? i recently had a game, where the enemy group had 1 platin and 2 diamonds, and my teammates had no league placement… what the hell is this?

Players may be on a winning streak during their placements or play unranked and have diamond MMR. Ranked and unranked modes are “merged” so you may play ranked match with unranked players.

3v3 and 4v4 are not really active gamemodes, so in order to decrease searching for opponent time, there are larger acceptable MMR margins.

3v3 is less populated so there are larger gaps in rank. The longer you are in queue the bigger a stretch in matching there will be.