I have the same problem! I made a thread on this as well.
Im plat I and I recently started checking out my teammates accounts post game, and learned i am constantly getting Bronze, Silver, and even UNRANKED teammates.
The only way I can win matches like this is to carry the team. I gain 12 and lose 12 as well.
I have a friend i play with sometimes, he has a better arenas ranked K/D, and win rate than me, and almost equal average damage, but he gets a minimum of double the AP points for wins than me, and also only loses -12 for losses. It makes no sense. I think its a serious matchmaking issue that started after the 1st patch/update this season.
It's incredibly upsetting.