To me, this just encourages DKs to use Death Grip prematurely instead of after the enemy uses an escape, such as Blink, Disengage, Displacer Beast, etc. You can use it to force those cooldowns but if they don't, that's 3 seconds of uptime before they do Blink away.
The pro I see to this is Double Gripping 2 melee DPS off of your healer. Pull Rogue, target and Grip Warrior, Chains root to prevent instant Charge. Any other pros I'm missing?
Next, I'd like to suggest new set bonuses. Personally, I like the idea of focusing on Death Grip but feel free to suggest anything for the set bonus to improve.
A few suggestions to get the ball rolling:
-Reduces cooldown on Death Grip by 5 seconds.
-Targets affected by your Death Grip are slowed by 60% for 8 seconds.
-When used at a distance greater than 10 yards, Death Grip disarms the the target for x(2-4) seconds.
-If Death Grip is cast while jumping or falling, you will instead be pulled to your target.
-Death Grip suppresses effects* on the target that allow casting while moving (K's Cunning, Spiritwalker's Grace, Scorch, etc) for 3 seconds.