So... personally I am not bothered by the fact that the most defining feature of Astrologian, the only part that is truly unique to the job, has had its experience enhanced in some way.

Looking at Nocturnal Aspected Benefic specifically, I don't believe there is anything inherently wrong with the way it provides a shield equal to 300% of the amount cured. The issue, in my opinion, is the base cure potency. For example, if the base potency was 140 (the same as the Diurnal potency) then a 300% shield would equate to a shield roughly on par to its value as of the 3.5 patch. The end result would be an overall nerf, but personally I rather like the idea of its use being more strictly focused on providing a shield while being less useful for directly restoring someone's HP because that gives it more of a niche purpose.

Addressing the issue of whether or not Astrologian should be able to heal equally well to a Scholar or a White Mage, my belief is that if anything should be weak it should be its AoE healing capabilities. It does raise concern when a Nocturnal Aspected Helios has a greater shield strength than a Scholar's Succor and by no small margin. Perhaps it would be less of an issue if Deployment Tactics could be used with a much greater frequency, which I think would better compliment the tactician style of a Scholar, but currently a Scholar can only provide a better group shield once every two minutes.

So no, an Astrologian absolutely should not struggle with keeping a tank alive, but if any part of its healing should suffer I believe it should be its AoE healing, forcing a greater dependency on a co-healer while discouraging an AST/AST dual setup.