I too can present incoherent arguments resulting from a deliberate disuse of reading comprehension, but I'll spare you the example.
The problem of tanks having enough in-house healing to obviate the role of healer is not solved by turning tanks into healers and healers into DPS with party support. That is so bewilderingly ass-backwards it makes me wonder if you're only defending the notion as a gimmick.
The solution, one that I'd be in favor of if we assume a frictionless spherical cow, as it were, is for the tank jobs to not have as much in-house healing. In fact, I for one would approve of a return to the older style where the big challenge of tanking was managing aggro, and then every expansion would give more tools for that rather than a continual escalation of our damage rotation. But it's unlikely I'll live to see that world, because for that to work and be financially successful CBU3 would have to abandon the increasingly tattered pretense that they don't want there to be a "correct" way to play a given job and actually have content sit people down and say plainly "cook or get out of the kitchen." Which they're already kind of doing with the newer jobs, but that internal contradiction still makes me laugh when I think on it.
The reason tanks have so much healing and support kit is because it turns out a lot of "healer mains" are dullards who can't even press Cure II correctly while a lot of tanks are tryhards. If everyone who wanted to heal was forced to demonstrate they are not in fact a dullard—a threshold that is better determined by people smarter than I—before being allowed to inflict themselves on the duty finder, such that tanks no longer could set their watches by how often they've had to save a run with their own healing kit, chances are good we'd be in a much more interesting timeline. Do the same for every role while you're at it, hell every job if budget allows. It doesn't have to turn everybody into a tryhard, but everyone should have at least been made to go through the motions at least once and grasp the theory on how to do things properly.
This is a dichotomy failure birthed from the death of trust. DPS only fixes the issue if you deal so much damage that the enemy dies immediately after their first auto-attack, if not before. That is not going to happen, so something else needs to be done to solve this.