ABC was considered suboptimal in older MMOs because the resource systems in those games forced healers to be inactive if they wanted to have sufficient resources to survive a fight. In FFXIV and many other modern MMOs, this bad element of game design has been fixed. From a logistics point of view it can be an interesting puzzle to balance idle time with active time, but it makes for incredibly dull gameplay. This is especially true when only one portion of the population (healers) are forced into this inactivity.
Allowing all party members to continually contribute to party success is not a bad thing. Neither is allowing players to play the game without their participation being severely restricted by punitive resource systems.
As the game is currently designed, (1) healers have many idle GCDs that do not need to be spent on healing. Depending on the healer and the group, this can be in excess of 90% of all GCDs. (2) Healers also do not have significant resource management concerns that mandate idleness outside of a few fringe scenarios. (3) The current toolkit that SE has given healers includes nothing apart from damage spells to use in these idle GCDs. The conclusion, then, is that healers should spend these GCDs on dps because there is a negligible resource cost to doing so and it provides a very significant bonus to party output. So long as this is the case, ABC will remain the logical conclusion for healers in FFXIV.
If any of those three premises changed, then healer dps may no longer be desirable.
If (1) changed by requiring more GCD healing (say, by moving some oGCD heals to the GCD) then there would be less idle time to be spent on damage.
If (2) changed by severely restricting MP as a resource then healer would be forced to conserve their MP and be unable to dps.
If (3) changed by expanding healer GCD options to include buffs or utilities that benefit the party more than that same GCD's damage, then healers would have other options to spend their non-healing time on.
I'd personally prefer a combination of (1) and (3). I can elaborate on what specific changes I would like to see if you're interested.