@OP's thoughts

You probably have enough input to make a decision here on what you'd like to do. As some others have suggested, I also suggest leveling all three healers as this will allow you to understand the nuances of each job and see what tools your co-healer can bring to the table. Also, variety is the spice of life and if you enjoy healing a lot, sometimes it's a nice change to change healing styles on more casual content to keep things interesting.

@AST Topic

If you look at absolute raw MAXIMIZE no holds barred MP-isn't-an-isuse healing, AST has something like 3% higher healing output than WHM in a six minute duration.

On a more normalized but constant and no-mp-issue healing, WHM wins by about 9% because of Freecure.

Because of Essential Dignitiy and Synastry, AST has a higher single target burst than WHM (even when you include for Tetra / Bene / Divine Seal)

Overall, I feel AST needs a change to Noct, however they didn't need to get the potency increase they got at 3.07 as your sect bonus already compensated for that.