No reason to ever have 2 dncs in a single pt. Why would you remove a whm... for a dnc?
What are you looking for in a tank?
Looking for the best hate holder?
Not dnc, sorry
Looking for the most dmg while tanking?
Not going to be dnc here either.
Looking for the least dmg taken?
Not dnc, either.
There's no reason to have a dnc tank. If you have 2 dncs, put them in diff pts and have haste samba active for 2 sets of DDs rather than one. If you have one pt, stick to one dnc.