The rewards aren't about the effort you put in. The rewards are to encourage role diversity because too many people are playing DPS. (Although I have to say, they really should have seen this coming when they made the decision to only implement two new DPS jobs in 4.0... just another instance of lack of foresight along with the VIT tank damage reversion...)

They are doing this because about the only other thing they can do to get more people to play tank/healer is to buff up the DPS of tanks/healers so that they are on par with actual DPS jobs. Which not only wouldn't be very balanced, but as a DPS you'd probably be even more upset about that than what they're trying to do here.