So I've really been thinking about tank rotations. For about 95% of all game content, it doesn't matter which defensive buff you put up. Sure they're slightly different, but aside from job-specific ones, the role actions are pretty similar (I'm cognizant of the Savage content knowing optimal combinations, but this idea doesn't affect that).

Convalescence could be a really helpful way for the tank to be able to boost up not only their own HP regain for healing, but the party as well if a big attack hits the full party.

Theoretically, this would not affect gameplay at all. Healers are expected to Cure III or revive folks faster, and a buff like that could add a little more helpful strategy for struggling healers to keep things interesting and offer more party-specific defenses. It wouldn't affect damage or defense.