Are instant-cast heals bugged?

Having reached 60 and received Tetragrammaton, I was astonished to learn that while it is affected by Cleric Stance (1k heal instead of 3500~), no other buffs affect it. So no bonus due to Defiance, Divine Seal, Fey Illumination, Convalecence ....

Would like a dev response as to whether this is a bug or working as intended, because it seems like a huge oversight. I'm told Lustrate is the same now too. I mean, Tetra is still useful but without the ability to buff it, it loses a lot of its utility.