People do commonly say that the main issue with the ‘holy trinity’ is the tank role. It’s unintuitive, unwieldy, and greedily snags a lot of the actual gameplay from PvE (ie. setting up pulls, et al).
But what my tank would really like for Xmas is a pet dps. I’m happy to run with player-healers, they’re usually pretty cool. But my game would be so much more fun if I could have NPC dps instead of players. Imagine not having to fight with your group all the time. Or people yelling at you to gogogo. Or people jumping straight into fights before you have threat because that 0.5s at the beginning is oh-so-important for dps.
Plus since your base character is a tank, it’d be tough enough to solo comfortably anyway. (And same applies to healers since they can self heal.) So really, if you have to remove one role from the trinity, it’s the dps that should go.