If your co-tank is pld then they'll eventually build up more aggro lead thanks to savage blade being in their dps rotation, so eventually yes you'll be able to fit some butcher's blocks.

On the other hand in drk's case they don't build up more aggro lead, so you can think of it as a ticking time bomb (until you overtake them, since even without extra aggro multiplier you'll likely outdps them, and using butcher's block will just shorten that time). From my experience even 2+ mins after my group's drk provokes the boss off me, I can still take aggro back using a single butcher's block.

I'm not disagreeing with you, I just want to clarify that you may or may not get that chance to work back butcher's block later after a tank swap if your co-tank is drk.