Q u o t e:
But I have to use it to use my cooldown.
Yeah, I think I have said before that this was not the intent.
We think it's still a good goal to have DKs who are tanking use different abilities than DKs who are doing dps. I don't thing tying Blood Tap to Vampiric Blood et al. the way it has been has worked out well however. That wasn't really where we were going with it.
I'm arm-waving here, but imagine a world where (say it in movie preview announcer voice):
-- Blood Tap finishes the cooldown of all your runes. It's on a 15 sec cooldown.
-- You can use Blood Tap for an emergency Death and Decay.
-- Neither of these are things you do rotationally, the way you hit Plague Strike, Icy Tough and Blood Strike though. You use them for emergencies.
-- These emergencies aren't super common because there aren't encounters where large groups of mobs regularly stream in that will one-shot the healers if they aren't tanked. If it's a large pull, sure AE tank that, but the individual mobs will die quickly. On large pulls with serious mobs, you CC the dangerous casters, kill a couple of others as quickly as you can, and have the tanks pull out a couple of the mobs, essentially tying them up too.
-- Likewise, Consecrate (especially Consecrate) gets somehow changed to a similar mechanic. Now nobody is just spamming AE threat moves to keep stuff stuck to them.
-- Imagine a Hyjal raid where the dangerous adds have to be tanked or CC'd, and then the weaker minions are just blown up with AE. These weaker guys don't have to be tanked because they won't one-shot a dps player (though you may have to Frost Nova once in awhile or whatever).