Just a bit more to do damage wise on the healers, nothing crazy

Make scholar a dot management healer
White mage could be like black mage and have some deeper mechanic with lily's that alters their spells
Astro more buffs? they already have the lowest personal dps so making this the healer to play if you want to be full support sounds good, just add more buffs
And sage, i'm not sure, but i'd like to see their damage-healing mechanic be expanded upon so it's not just the scholar fairy in practice

Just my 2 cents on what they could do