You're misunderstanding what I'm saying again. I never said that CDs are for restoring health. That makes no sense when most CDs reduce incoming damage or completely negate it! D: (Lay on Hands being the exception.) However, if you don't have a CD, then you can use a heal instead. Arguably, it doesn't matter what you use as long as you don't die. However, plenty of tank aficionados are more than willing to argue over what's the best CD at the best point.
Sorry, I read that wrong, as in pop a CD (not a heal) when you hit 20%.
I've barely tanked on my Paladin in WoD, but I still don't recall it healing for much, and it definitely didn't do a lot before. Unless it saw massive buffs or if the gear differential matters that much, it was completely worthless for me to use.
Also, keep in mind that there is no "basically replacing" WoG. WoG is gone. Prot Pallies don't even have Holy Power anymore.
WoG is an incredibly strong heal. Resolve, the replacement for vengeance increases self healing done and self bubbles as well as threat.
Currently: WoG heals about for 50% every 12-15 or so seconds at the expense of HP on another holy shield. Heal for more if you don't use it as often.
Legion: Use this new spell healing for 50% every 12 seconds w/o the opportunity cost of your active mitigation, because HP is gone for prot.
It's basically the same thing w/o the active mitigation trade off, aka a WoG replacement. It's fine.