Ive done this fight 128 times. Maybe 5 of them I was playing AST, the rest were WHM. I’ve carried so many bad SCH/AST that never shield. All I ever hope for is shields. I can do the heavy lifting, just help me out a little bit and put a shield on that tank about to take Tera slash in dps stance with no cool downs.

I’ve learned to network a bit. I let my co-healer know when they’re doing a great job and I add them to my friend list. Next time I need a solid co-healer I check my friends first. This might work for you too. Otherwise the solution is probably doing it with your friends, FC or maybe a static.