Balance 20% isn't used that much you know.

10% on the whole party is better actually.
And everyone like it.

"Because AST buffs single handedly destroyed WHM and ran it out of the raiding scene, which is not "fine"."
=> I'd say that it's good. Astrologian were so badly design at the beginning of heavensward that he has been left aside until 3.4 raiding scene.

White Mage was here since A Realm Reborn.
So it's good to see Ast was finally a good viable healer.

White Mage still is a good healer and strong healer. He'll probably get some unique buff in Stormblood.