Simple fact:
In pvp you need bursting, such a warrior would not have it, in pve you need sustained dmg and some burst from time to tine... maybe he will have it. Don't really know. This changes 1 skil for now from defence to some X dmg and knockback. So its not making this spec DPS for PvE and if it is it will be not working at all or overthrown fury/arms because the amounts of CC you get and mobility.
Remmeber 20 sec time Shockwave ? when you were able to literally sit and smash shield on enemy head and stun him and slowly kill him without him being able to do much ? Thats how this new skill sounds, taking and fork (low dmg) and stabbing (stunned) person to death. It will be either OP or garbage and it will be impossible to balance.
But in case of tanks it is easier to balance eg. Paladin tank is OP and druid tank is meh because of what blizzard made as a mechanics for them. Why nobody complains about this. It is super easy to create "balanced" in such terms tank spec/mechanic without much pain. Especially you have Metamorphosis form and if you wil go back in time to WOTLK and Cata we could even if we need more skills us them. We always since meta came in had those tanking skills, if its a problem with 10 yrd demonic leash, make it melee range or just make us use touch of chaos. I can draft a solid tanking spec and build for warlock and submit here just so you can see/judge if it would work or be crap idea.
I think You are a smart person.