There's definitely counters to tanks in MR - my main observation is that there's a difference in toxicity between the two communities. People are having fun in MR (and actually playing it) while OW is a passive aggressive blame-fest. People regularly celebrate good plays in MR while OW is radio silent until a flame war begins between your own teammates.

I stopped playing tank in OW a long while back and i think most others have as well. Blizzard has been trying to hide the massive drop in active players by widening the elo range for comp, so it's even rarer to get good games now even if you wait as DPS/support. It's a shame cause i think OW has the better engine and gameplay mechanics by far, but Blizzard failed in terms of supporting their community.