Actually it is their best heals.Except that that is sort of wrong, they have that one 'spammable' heal, but those are NOT their best heals, they can rely on it until you lock it out and THEN break out a big heal to make up for getting interrupted. Example: You interrupt dark Infusion, they then cast innervate and heal for an ABSURD amount more. Same with commandos/mercs who then go to their faster heal with the cd, Then rotate back to the basic heal, in a pinch there's still popping their 30 stack cd too, it's just too versatile. It needs to be a more far reaching lockout like wow to really have any effect. Yeah, with 4 interrupters you can keep someone locked out, but that's way too much dedicated resource to preventing a single healer from doing their job.
Innervate/healing trance only heals for a bunch if they have the HoT on and they crit each tick. (probably easier in pvp gear)