I perfectly know what I'm doing. I've been playing DK since day 1 of wotlk, and even though I'm far from being a hardcore gamer, we've cleared Heroic Ragnaros 25-man before 4.3, and 8/8 DS 25-man, which is arguably the biggest challenge a tank can face right now on live. Yadda yadda...
Besides, I personnally never said our AoE was bad. We're just having issues when it comes to unplanned events.
About downtime, honestly, I don't think it's as bad as we make it sound. Having a little is fine, because it helps us with timing our death strikes.
All in all, it is just about this inability to react on demand. As long as things go according to your plan, it's fine. If several random mobs or spike damage get in the way, you're screwed unless you pop ERW. Of course, you can't do that very often, and that's in my eyes a problem.
Adding back a way to refresh a rune or two on demand (old blood tap / new blood tap with 10 charges and no gdc) on top of having an actual rune regeneration talent like RE or RC, would not only solve this unability to react to unexpected damage or adds, but also fill this little downtime we have.