Worth mentioning that some healers will have higher single target DPS than tanks if they don't have much healing to do. Like a shockadin with CDs lined up. Mythic + (at least early on) seem to be all about AoE though, and it's really hard to compete with a tanks AoE without also being squishy / dead. BMs hunters do great DPS, but then you're managing a tank in melee range, 3 hunters at range, and a healer in either melee (pally) or range and I think movement is going to be a nightmare.

I think 1 x Blood, 3 x Frost, 1 x Shockadin could give current 5 x Tank setups a good run for their money, but will be harder to play.