If you are tank healing 70Ì€Ì€% of the time as you say, why not just spec disc?
I am 90% of the time already, still prefer holy at some fights (e.g. Twins where shields are near useless).
Maybe just use GS on him in those cases?
Because it has 1 minute cooldown at best and we often use it as part of our strat.
Ayreons comment regarding speccing disc is a good one. Still, I am interested as to why you choose to run as holy in that setup. I have been only running 10 mans for some time now, and beginning with Ulduar hard modes, I have moved - reluctantly - from switching between holy and disc to disc only.
My impression still is, that in most places healing as disc helps a 10 man raid more than healing as holy - except if the other healer already is a holy priest.
This includes places like Freya+3, where 2-healing as disc in a 10 man equipped T8 raid in combination with a holy paladin sounded insane at the time, but ultimately turned out to be much safer than holy. Sure, overall throughput is lower, but death prevention seemed to be worth more.
That said, it is a long time since I have tried sustained tank healing as holy. Is your opinion/experience that this is now sustainable with mana pools in T9 content?
Well as I said it's all about your role and the setups you run with. My role is *very* versatile (usually compensating crap healers in ToC10 normal, or ToGC10 with 2), but I'm never a pure raid healer since we almost always have a druid or other holy priest. I also do mainly 10 mans as it is an alt. Doing the compensation job I'm more holy than usual because, frankly, sometimes the throughput of disc is simply lacking (I'm thinking Jaraxxus e.g. where the debuff isn't healed through fast enough, or Twins). Granted, we could take less crap geared people, or I could smack the dps everytime they stand in fire too long, but it just doesn't work like that and especially not with alts.
Maybe I'm a control freak but I cannot justify a tank dying now and then - even if I'm not tank healing! - all because I couldn't deliver enough throughput with FH (and/or PoM). I just like to be that versatile. As said I can perfectly accept raid healers dropping it, however, if you'll be (support) healing a tank even 5% of the time, I can't miss it. In 25 man raids it's much easier to rely on some palading sniping some heals doing your job. Which was kind of my point, do you run 10 or 25 mans mostly, only normals or hardmodes, how are the other healers, how's the setup, etc., this talent's value is imo very dependant on that.
As for holy's viability as a tank healer, it's not that bad really, I feel it's just as stable as Disc if you know the fights (being Disc it's a little easier to just heal reactively because Penance just is that good
) albeit a little less mana efficient.