Astrologian has never moved towards or away from a standard healer template since its release. It merely gained power, both to raw healing and to (though reverted in SB) card potency. Its problem was that it was undertuned--nothing more. It likely could have been far less "minor variant to template slot A, minor variant to template slot B" and still reached a competitive state in 8-mans so long as it was properly tuned.
Why was Astrologian so desirable around the end of Heavensward? Because it was the go-to example of overtuning, the devs having classically overbuffed the toolkit in place of fixing its mechanical issues (e.g. Extend generally being useless with any Spread ready due to the added duration being wasted, weaker card effects overriding stronger, etc., etc.).
I'm wholly aware of short- vs. long-term benchmarking and the disadvantages a indirect contributor or primary output (i.e. rDPS)-focused job specialized categorically towards short-term goals (healing) can face during early progression and that its competitors would face during post-progression, provided there is imbalance between their growth curves or the distinct job attempts to make itself distinct by niche, rather than gameplay. And yes, there is imbalance over time in every example by which you might compare indirect and direct contributors in this game. Whether it's Ninja versus Samurai, Dragoon versus Black Mage, White Mage versus Astrologian, one side sees far higher rDPS consistency, while the other strikes that equilibrium in one comp, pales to it in another, and renders the competitor obsolete in yet another. That is the way the game works already, due to unintended issues of scaling. If that's not acceptable for new job concepts, then it shouldn't be acceptable now either. The scaling procedures need, then, to be fixed, to see far tighter total-throughput consistency across jobs.
The bottom line is that I don't want to be a minor variations on a Tank template (category A+2, B-1, C+1, D-2, E+1, F-1). I want to be a Paladin, a Warrior, a White Mage, a Scholar, a Ninja, a Samurai, etc. Even where specifically-defined or categorized parity is desirable, it can come from original conceptualizations, rather than patterned noise laid over a template. I feel it's important to allow the widest possible range of content to each job -- and to find distinction by gameplay, not niche--but I have no issue with finding x job more desirable for x set of mechanics. I'd much rather the game actually take their "all jobs on one character" concept and run with it, rather than attempt to make the experience made for and by each job interchangeable. We've never played less than 3 jobs at a time in any FF single-player game, and with quick access to the whole remaining roster, with whatever advantages and disadvantages they may have. Why should we go unpunished at all if we choose to, let alone encouraged by weekly caps and level-proportionate rested bonuses to, tunnel-vision on just one job per role, sacrificing our own and others' plethora of experiences otherwise available in seeking overspecific benchmarks of parity (and being wholly forced into design by template to meet those benchmarks)?
Hell, insofar as regular content (or really anything but fixed, "cutting-edge" content) goes, you can look at some of the compositional scaling systems WoW and a couple other MMOs have been working on: if a given healer provides only 7/10 the "standard" raw healing, the challenge retunes the raw damage output to something just barely manageable given the utilities across said healer, the DPS, and the tank, and excess of role-specific traits on the tank himself. Different experience, with as close of parity in intensity as two runs of the same standard composition by different players.