I am not good with math, but I give it a go!
With my gear (478) I get these numbers unbuffed, without stance (except for Sanctuary itself ofc):
Sanctuary 1500x15 ticks=22500x6 targets=135000 healing for 18900 mana (in the best of worlds where the raid stands in the same spot for 30s constantly taking ae dmg I guess?) No mastery on this spell. Often a lot of this goes to overhealing since stacking in AoE don't last 30s! 7hpm (I would say more like 3-4hpm)
PoH=30000x5=150000*15% (mastery) healing for 13500 mana. Also usually a good portion of this goes to overhealing. 12,7hpm.
CoH=16400x5=80000*15% (mastery) healing 9600 mana. 9,8hpm (Best about this spell is it has very, very rarely any overhealing so I still think it's ok with 9,8hpm)
PoM: 21000x5*15%=120700, cost 10500 mana. 11,5 hpm.
Notice I make these calculations WITHOUT Chakra (15%, soon 25%) wich would make PoM, CoH and PoH a lot stronger aswell, giving them 15% (25%) more hpm, wich makes Sanctuary look even more unattractive to use.
So, in my eyes, Sanctuary needs atleast a 150% buff, to be worth using with the current cost. They could rly buff it 300% but increase manacost then. It would give 4500 ticks with 6 or less targets every 2s. I don't think that sounds like overdrive at all^^
*reserveation for severe miscalculations