Ohhhhh buddy, do I have news for you.
In a raid scenario, a WHM that can gain a buff from keeping regens up will no doubt 100% absolutely keep them up for that buff. Even if it means stealing aggro. All they'll do is blame tank aggro, and tanks will ask for aggro buffs they don't actually need, and Ninjas will become even more prominent for their aggro utility.
Not to mention WHM will go from a healer to a regen spammer that slaps on regens and watches everyone die to deal dmg.
Of we're going to add dmg utility to WHM, it's can't be tied to it's heals. It either had to play off of Cleric Stance or the DPS skills themselves (ex Aero ticks have a chance of making Fluid Aura reset).