Yes being consistent is the key. Astrologian needs one thing really and that is the ability to move between noc and duirnal stance in combat through some method. Noc is the answer for Astrologian's ability to keep up with white mage for emergency situations. And you left out synastry along with being able to buff our own regens an extra 30% on the tank along with also ES would most likely be up again by the time you use up your other cooldowns.

If by then shit is still hitting the fan then all of these worst case scenarios would spell a wipe then you need to look at other factors. Yes I am aware you are trying to set me up in a corner to claim that bringing out a white mage would be factor but in a worse case scenario emergency healing should not happen more then 3 times a minute at most and Astrologian can cover that as well as a white mage can. And more precisely an astrologian would do well to be in nocturnal stance to support emergency situations over trying to be a slightly weaker white mage if you are using a white/astro combo.