White mages heavily focused on over-time healing. Regen as a long duration, smaller heal, a new short duration (3-4 ticks) regen with significant healing per tick, medica 2 turned into a group regen, and direct heals that add regen effects as riders. Smaller group damage potential, but hands down the best efficiency and throughput.
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Scholars heavily focused on shielding effects. Heals with shield riders, shields that are just shields. Group shields. Eos and selene tweaked around the utility they can provide. Cooldowns to fully shield the next hit. Mitigation focus over restoration.
Astro healing changed to time manipulation. Current heal set removed. Cards added as longer cooldown abilities (not random) that do an on demand effect (mp regen, shield, damage, crit, speed, as current) and a secondary heal effect. Short cooldown to extend card effect. Short cooldown to enhance card effect. Long cooldown to freeze a targets HP from changing for a few seconds.
New healer:. Has several damage skills which cause party healing, either as a group pulse heal (instead of healing for x potency once, it heals for 3 hits of x/3 potency) or as a direct heal. Its traditional heal line heals X potency, but if anyone else in the area is damaged, it bounces to multiple targets, healing .7x, .25x, .15x potency instead (initial target, most damaged, second most damaged in range). Provides more offensive buffs to the party, but has to have damage uptime to heal to the fullest, and lacks impactful mitigation qualities.
Ideal composition is one of the first two + one of the second two, but the toolkits are robust enough where content would be doable by any combination of two.
Theres still design space for a few more healers in there too. I cna give you ~6-8 before they overlap, and thats keeping it limited to what 14 can handle mechanically. If you let me work with what other MMO's can handle, I can give you 12-14.