There are unfulfilled stat combinations that many full service supports (those that are dedicated to boons and healing) might benefit from. Main healing power or concentration, with the other as an off stat, and vitality as the third stat.
Existing stat combinations with both healing power and concentration work, but aren't ideal. Harrier is main power, which is of no significant benefit to dedicated healers and pushes the support stats down into the secondary slots. Giver's suffers from the same issue while also affecting aggro in some fights (fine if you're the tank, but otherwise problematic). Minstrel is more flexible than giver's but still pumps toughness a lot. Plaguedoctor is nice as a building block for hybrids but doesn't give enough conc/healing power for dedicated supports.
Can you make do somehow with what's available? Certainly, and I have done so for 3 years of raids, but I would immediately switch over to Con+Heals/Vit or Heals+Conc/Vit if either were available. Those are the only three stats that I want as a pure support, so it would be nice to see them all available in the same package.
Like it or not, role specialization is here to stay in endgame content and it would be lovely if support mains got a proper stat combination for their jobs--something that isn't main toughness or a DPS stat.
(Purists can argue that vit is "wasted" but the dps increase for healers from unfocused dps stats is trivial and toughness produces the aforementioned aggro problems. So outside of speedrunning, vit seems like the least useless of the three for a pure healer. More options in this case to suit different purposes would be better.)