Stomps happen all the time its just part of the game. They may not always be 12-0, but more often than not the match ends in 12-4 or worse. It is just how the game is, once a side takes a lead, it is like a snowball effect. This is because a mech at 50% can do as much dmg as a mech at 100% (assuming he didn't lose any weapons). So once a team loses a player or 2 it just becomes progressively worse after that. The first few kills are often the decision makers for any given match, it is very difficult (though not impossible) to come back once you're down... thus these constant 12-0/1/2/3/4 matches. It's not really an issue though because, unless you're extremely unlucky, you aren't always on the receiving end of these stomps. Some nights it may feel like it, but we often forget the matches where we stomped the other team since they end so quickly and you rarely do huge damage or anything memorable in them.
What grinds my gears are games like my screenshot below. I am close to if not the top match score in the match but due to awful teammates we lost anyway. Those are the worst because you think you are doing good but next thing you know its 6-0 and you know its only a matter of time til you get jumped by 12 mechs.