I've said it before, I'll say it again - counter argument: Mt. Gulg and Amurot. Both required MSQ dungeons that are still decently difficult even now with certain pulls (minus boss fights) and are arguably harder than any other lv80 dungeon we've gotten thus far. Could've easily made all 80 dungeons around Amutot's difficulty, but didn't. Why is anyone's guess.
Also, we have all of these healing tools as healer and quite frankly don't even need half of them.
I can count on hand the amount of times I actually needed ES, Horoscope, Neutral Sect, and Collective Unconciousness in anything (read dungeons). If I wanted I could literally use nothing but Celestial Opposition, Essential Dignity and Helios for most content (and probably have more fun doing so). We have too many healing tools.
They have options to fix this: up the difficulty in content so we actually use them all (which they can do without making things impossible for players to complete), remove some of our heals (and replace them with utility or dps), or if they want to keep all of these abilities change their mana consumption and lengths of cool down (make piety actually useful!).