The problem lies in winning.
If 1 side wants to prove they don't suck shit, then they can do just that. "Winning" doesn't prove you don't suck shit. You just need to play at a certain level. If 2 teams of "noobs" played each other, regardless of the outcome, both teams are still "noob". If 2 teams of pros played each other, regardless of the outcome, both teams are still "pro". Winning just proves that your team is better than the other team.
So do just that. Play the match, and depending on how well one team did against the other determine the skill level. Assuming team A is pro... If it was a crushing defeat for B, A has a full bar left, you could consider B beginner or "noob". If they chipped off 25%, they're decent. 50%, good. 75%, very good, probably near on par. If they won, really good pros (Depending on the margin of win.)?
In any case, you need to have an idea of what type of playing is "pro" or good, then compare it to yourself or others.