I don't see why, once you've learned the content, that you wouldn't want to maximize DPS as a tank. Priority 1 - hold aggro. Priority 2 - mitigate when needed. Priority 3 - DPS. Holding aggro is ingrained in the tanking jobs from the first dungeon. Mitigation comes with learning content. Once you know the content, you're selling yourself short to not try maximizing DPS.