You're so cute. SE has in fact stated that they take the DPS a tank can do into consideration when designing content. They encourage tanks AND healers to also dps. Just because you're a tank doesn't mean you shouldn't still pull 1k DPS to down the boss faster. As has been said to me before... the faster the boss dies, the fewer attacks he does, the more you have mitigated. Your narrow view simply means a narrower understanding of mitigation. Your VIT trinkets do not provide any form of mitigation, only survivability. If the fight has big tank crunches that hit for 15k, sure, your VIT trinkets are necessary to survive. But unless this is the case, then they server no other purpose than to inflate your HP pool and the boss fight lasts just that much longer due to your lack of higher DPS.