I feel like part of the reason tenacity doesn't add more to damage mitigation is the majority of the game appearing to be toned to hold people's hands. The enemies damage is scaled back in party duties because they don't want the squishy non tank people running the risk of getting 1 shotted when they stand in something they shouldn't or run off ahead when they shouldn't drawing aggro. Because of this more people get to the point they look at nothing but their DPS and don't bother with anything else. That said it hasn't stopped me from running skillspeed/tenacity melds with DH as the backup if I cant get full materia bonus on the first 2 stats. It just feels better to me. Then again I don't run a parse and don't really care about dps unless I'm in a situation where I can visibly see I am doing more damage as the tank than the DPS in my party.