Needs to be more. Before Exodus crashed, throughout all the roulettes I've queued for, bonus was for tanks, tanks, tanks. Rarely see Healer bonus, and even fewer DPS ones. Yes, we need tanks in dungeons, but someone has to keep them and the DPS alive. Constant Tank bonuses has led from what I've seen, an increase in tanks played by players who have no business being tanks. They want that bonus is all. WE have to suffer their incompetence and try to heal past it. My poor Eos has taken far too many beatings today, yet she kept hate better than the assigned tank. You'd think she'd get a bonus for that.
Overall, I'm suggesting spreading the wealth. Healers and DPS enjoy bonuses too. It's not all about the tank.