How can tanking and healing be made more broadly useful in more "role-specific" ways?

[Reynhart]

I'm not sure I understand the last bit of your post - if you aren't being killed by enrage and you aren't being killed by your healer running out of MP then what is supposed to be killing you?

The fact that the boss' DPS should be higher than your healers' max HPS.

And what adjustments, compensatory or improvements in their own right, should DPS feel in order to make that vision cohesive?

DPS should do much more damage, thus gain more enmity, to the point that enmity management is a real concern for the tank if DPS go full power. But, with a good tank, it would be very satisfying to unleash everything you can as a DPS. Like how tanks could manage Sneak Attack/Trick Attack or Ancient Magic Burst in FFXI.