A healer in this game, when you think about it, can be broken up into two main elements: a healing specialty, and a secondary feature.

Healing specialties simply refer to whatever "special effect" is tacked onto a portion of non-basic healing skills in a standard healing toolkit. This is pretty simple to spot via what kind of heals a particular healer job is known for, so HoTs for White Mage, shields for Scholar, and alternation (picking either HoTs or shields) for Astrologian. Typically, a healing specialty is the element which a healer job relies on to both perform its role and to stand out among others in this role. Other examples would include Delayed Heal Triggers like Excogitation, Escalation (heals leaving buffs increasing the amount those heals heal for), and even Periodic Absorption or "Shields over time".

Secondary features, on the other hand, are elements that are usually associated with damage dealt on some level or offering a degree of ease on healing to provide more damage as a healer, but are mainly designed with the purpose of keeping a healing job unique and at least somewhat interesting. For White Mage, this would be extra damage via spells and abilities such as Assize and Afflatus Misery (which I still prefer to call "the fart bomb"). With Scholar, its secondary feature is indirect healing in the form of its fairy, which despite seeming more like a healing feature, is intended to offer ease in healing for the job to do more damage with its basic damage toolkit. Then there is Astrologian, who has its card system that allows for (at least in theory) a means of increasing damage of allies to offset for what damage it can't do. Healing via Damage is a really good example of a secondary feature, as it can offer an ease in healing required and promote damage while not being as broken as it would be if it were a healing specialty (since that means it'd have to be more relied on, resulting in massive balance issues). Other forms of indirect healing such as totems are another good example.

From those two things, you'd follow the basic healer kit shared across other healers:

Basic heal
Large heal
AoE heal
Instant heal
Specialty heal
AoE specialty heal
Raising spell
"Increased healing" cooldown

Basic damage spell
Periodic damage spell
AoE damage spell

I could probably fill it out more, but kinda nodding off. Anyway, after all that, add in some any spells or abilities that would "round out" its overall kit and voila, FFXIV healer.