I know I have mentioned this in another thread, but an easy fix that would be relatively simple for the non-existent development team to implement would be to simply limit the pool of heroes who could potentially show up in a full mirror to those that people actually enjoy playing in that mode. I assume Blizzard has the stats on which mirrors get played (Thrall tends to always have everyone participate, in my experience) and which are most often left (Genji, ew). They could also do polls in Reddit to see what people tend to have fun with. I know I would vote Thrall, Kerrigan (waaaaaay too much fun!), Nazeebo, and Ming (aka, Dodgeball on steroids).