Maybe because I always pulled 3+ mobs, never less. If there was a patrol of 2 mobs running around, I was proximity-pulling them, then run into another pack of mobs and burn them down. The self healing of blood allowed me to pull all kind of stuns. The Improved Blood Presence + Rune Tap + every mob which died was giving me a lot of hp, chain pulling was no issue. But while playing Unholy for a short while, the PET was somehow getting into toruble with 1-2 mobs and getting killed. Ofc, not every pull... but anyway, I just enjoeyd blood too much.
And yes, the advice is try each spec for a couple of levels, since you are lvl 70, you can have fun with all. In fact, leveling a DK is not a matter of time, unless you are really bad and keep needing bandages and stuff after every pull, it's a matter of having fun. Sometimes I think about making another DK just to try whatever I have missed doing while I leveling my first one.
I am having my fare share of Unholy playing now, in ICC, with my pet alive all the time unless I die.