Certainly, and I will give the Dreadlord this, the DL provides a much higher return at level 6 than the DK does. However, the DK provides overall more use at level 5, which is the level most primary heroes reach in basic games. At level 5, the DK gains access to one of the game's nastiest sniping weapons, and trust me, there are lots of players that hate my guts for Coiling their heroes every 5 seconds. In addition, he becomes virtually uncatchable at that level, because he has Unholy Aura, combined with his fast speed. With even one point into Unholy Aura, he is the fastest hero, and with all three points into Unholy Aura, I believe he hits the speed cap of 400 movement. Good for dancing, as the DK does require quite a bit of dancing. In addition, starting him up as your primary has quite a reward, since he can be used to tank for the army during creeping and, more importantly, in combat. Death Pact ensures that he will survive longer than most heroes (barring a Paladin with level 3 Divine Shield), and be around to Coil his fellow heroes and units back to good health.
Concerning Death Pact vs Divine Shield, I've come to accept that Divine Shield is far better than Death Pact, rather than allowing the DK to serve another purpose, but it's likely that this is because the DK would be far too dangerous a hero if he had something like Divine Shield. Death Coil already has a faster cooldown than Holy Light by a full 3 seconds, meaning it can be cast more often, allowing it to be spammed on enemy heroes or your own units, and having the DK run around unchecked for a full 15 seconds via a Potion of Invulnerability is a nightmare enough for most players, though I imagine a Lich with that could cause far greater headaches/nightmares. Nevertheless, giving credit where credit is due, Death Pact remains the only spell in the game that directly heals the hero himself, and it's pretty damn good at it too.
