Deathgrip is suitable as an extra, maybe, sometimes taunt.
Try it sometime. How many bosses does it work on? At best, with most it works as a taunt. At best. (Charge, on the down side, has the unfortunate side effect of generally not stunning most bosses, and giving them almost one free shot at a warrior's back)
Even on a LOT of mobs in dungeons I see the word "IMMUNE" go flying up often enough where I generally only use on trash that I KNOW
for a fact it works on, or I save it as my last ditch "OMG I GOTTA GET THIS MOB OFF MY HEALER" butt-saving tool.
Oh. It has one other use. Ranged interrupt. IF it can pull a caster-type mob, it usually will work as an interrupt.
It's not a very consistent tool though compared to dark command/taunt, or charge, or intervene.
All that said................................
Mobility needs to be addressed in how you approach an encounter. I'm not going to handle an encounter with my DK the same way I would with my warrior. In some ways, yes. Pack of mobs?..... Lay down an AoE threat gatherer in order to grab the group. I shouldn't even be saying this as it should be common sense
Also, you have to take into account the group's play. Do you have a ranged dps'er who is targeting off your target? And is they do, what do they do when they pull that mob off you? If they can burn it down before it gets to them, fine. If they can't... what is their next action? Does the mage hit invis? Does the hunter feign death? Or..... do they keep attacking it and run away from you screaming "GET IT OFF GET IT OFF GET IT OFF!!!!"?
A good tank will look at the situation and make a good decision. In the last case presented, if they run it out of range and me moving to pull it back could result in a wipe... hey, sorry... your poor dps play isn't my fault and I am responsible to the other 3 people to give them a chance to survive and be successful.
Now granted, if they're close, I will TRY to taunt or get the mob off them. But at what point do you draw the line? The first time? Second? And, do you have the balls (or ovaries) to tell them, "Hey. You need to change the way you're doing this. At least, if you like surviving."
Alright. Getting too long-winded and blah blah blah. Think I made my point.