Tanks and healers indeed do have similar playstyles between themselves. Maybe I'd say GNB strays a little from it... I was also kind of let down by Sage, as it falls into the same spot as GNB but for healers, there's no actual meaningful divergence. I wonder if it's because of the roles?

DPSers are way ahead on that spectrum with more diverse playstyle despite the builder/spender mechanic repeating in some of them.

I do think the homogenization of party buffs is indeed being unified after Ninja's change.