Of course there are matches that you can't win no matter how well you play.... even if you would play like a god. But those are around 1 in 20 maybe. In many games it's possible to compensate for unfair matchmaking, for example if you squash the opponent on your side and then flank the other side to help your team.
"Doing alright on your side" is not enough to win an unfair match
Exactly that is how I do it as well you crush your enemy your side then you rotate to your mate side and do the same thing there , also it does help their mental quite a bit when you tell them pios down gren down etc..