Yeah the OP didn't ask about DKs but perhaps he just didn't consider them

As far as runners, with a DK you have many options: Death Grip, Dark Command (ranged taunt 8s cooldown), Icy Touch, Chains of Ice (won't pull aggro but will slow the mob to 10% lol), Death and Decay (heres where it shines compared to consecrate, you could throw a DND right on top of your slaves without having to move your tank and all the mobs attacking your slaves will come to your tank), and if you catch a runner RIGHT away, you can use unholy blight to damage him while hes still near you which has a good aggro generation. Also, pestilence will jump up to 15 yards and if you're close enough thats enough to put a couple diseases on the runner and possibly have him re-aggro the tank.

Aside from that, I think the DK has better oh crap abilities because they don't rely on shields and can be good for PvE and PvP: Bone shield, Icebound Fortitude, Anti Magic Shell, Anti Magic Zone, etc.

Its true, playing a DK while multiboxing (and while solo boxing actually) takes more skill than playing a paladin for sure (and maybe a warrior), but it doesn't cause me any issues and I suppose if I didn't have enough skill to tank with a DK while multiboxing I probably wouldn't box at all because many things would just be too tough. As it is, I think its not that difficult at all and I like having the extra options rather than the "4 paladin buttons" should I want to use them - even if its not a requirement.