Despite being the stock arcade game mode besides death match, I think it’s absolutely one of the weakest. My overall experience with it has been a very negative one, and I’ve had plenty of time to experience it.
The way it always feels is that one team will receive an overall effective composition whereas the other team will receive one that is comparably ineffective, and that matches quickly become wave upon wave of one team throwing themselves at the other in the hopes of wiping them; usually to no avail. Alternatively, the compositions of the teams ebb and flow until one team simply settles into the stronger comp, but this situation is still one that’s hard to overcome for the opposing team, outplays or otherwise.
It would be nice if there was some sort of algorithm in place that could determine that maybe it’s not such a hot idea to give the team desperately trying to push with no healers or tanks its third, active Torbjörn. Or likewise, perhaps the team with multiple heroes on fire with active killstreaks don’t necessarily need a Mercy to rez them when they’re finally picked off.
I think the game mode could work with randomly assigning each team any combination of 2 Tanks, 2 Healers, and 2 DPS; it would still require players to be flexible, like the current version, but it wouldn’t punish either team for not having essential roles because the digital dice didn’t roll in their favor.
Regardless, I think the negativity bias for Mystery Heroes is a bit steep to keep it as the stock arcade mode; I think something like No Limits is a lot more agreeable for a lot of people, as people have an actual choice to effect and control the outcome of a match.