It's almost funny how value of DPS trackers changes depending on the point of view. When seen negatively the defenders will dismiss their "power" but when shown in positive spectrum they'll go into overselling them. Personally I don't care about them too much but I don't believe community as whole can use them. Ultimately Damage, DPS however you want to put it is the end result. All you know is that X did too little damage. But why? Was the tank not keeping the boss steady which resulted in Melee DPS having to adjust their position and miss their GDC? Were the mechanics simply a counter to the BLM? (Extreme Navel says hi). Were Red Mage or Summoner busy reviving medics when they died? Was the tank doing poor job at mitigation which forced Healers to waste everything they had to keep them alive? While decent statics could probably figure those things out any less coordinated groups from PF and Duty Finder won't be really able to utilize the info in any constructive way. Making them integral part of the game also expands their reach into areas it's not even needed like Dungeons, Normal and Hard Trials or regular difficulty raids where "perfection" is not required. I won't say people don't use it there but I also don't think it's widespread.

There's also one risk I can't properly overlook. That damage will become goal in itself. Even in cooperative experience there are more than enough players willing to treat it as competition. And while I see nothing wrong with two teams competing in things like World First Clear of content or later the fastest clear I don't think there should be anything that incentives players in same group competing with one another and I'm afraid that this is what would happen if damage tracker would become widespread in the less punishing content. So yeah personally I see to many risks and really not enough rewards.