Sortof–these are rough numbers based on testing on self only, without benefit of 5-man buffs. I have 88k mana, self buffed only. Assuming we’re about to enter a high AOE damage phase of a fight, if I want to benefit from Symbiosis (resto druid mastery), I have to blanket 5 people with Rejuvenation then cast Wild Growth for effective AOE healing–which costs me 22k (25% of my mana) for the Rejuvenation alone plus another 4.5k mana for WG (5% of my mana) for a total cost of almost one-third of my mana to heal one AOE phase. If you add in popping tree first (~900 mana) and finishing up with Tranquility after the rejuv/wg blanket (5.4k mana), and we have a whopping 37% of my mana gone in about 20 seconds. Far more expensive than group healing in Wrath, for sure.
However, that 37% of my mana results in a per person heal of roughly 90.7k each at my present stat level (assuming self buffs only). Even if the AOE is hitting for 5k/sec for 8 secs like the Anraphet encounter, that’s still a net gain of 50k for everyone. We, in limited circumstances, very clearly have the throughput to keep everyone alive.
The problem lies in if you have a fight with more than 1 of those AOE phases. You lose out on a second Tranquility (8 minute cooldown) and maybe even Tree of Life, if it occurs before the 3min cooldown is up. So for phase two AOE, you only output about 23.3k health per person, while everyone LOSES 40k of health (again, Anraphet), for an effective loss of 16.7k health each person. Which cost you another 30% of your mana.
2 8 second AOE phases can cost you 2/3 of your mana in a single fight. Of course, none of this takes into account the amount of heals you’re throwing between AOE phases (nourish/LB with an occasional HT if you’re lucky and only the tank is taking significant damage), or is it taking into account your in combat mana regen rate (1.9k MP5 for me presently, self-buffed), but you get my point.
We’re not ineffective group healers now, but it does cost an arm and a leg to do so now, particularly in longer fights.
Disclaimer: I am not an expert, my math may be wrong, someone is likely about to come along and prove every point I’ve made wrong, etc. 