Tbh, stance aren't really tank stance and DPS stance as much as a defensive stance and offensive stance, the monikers tank/ DPS stance is one the players decided to call as such.
There isn't anything fundamentally wrong with this game, it's just a more modern approach to the tank/healer/ damage dealer trinity. An approach that makes both tanks and healers considerably more enjoyable than spamming 1 2 3 or being nothing more than a healbot.