That's still a damage loss, and that Unchained could've been a Fell Cleave. :V

But I guess if you don't know if the other tank knows how to drop threat, for safety, you should go into Defiance and Unchained. So fair enough. Still, I'd highly suggest dropping Grit @ 4~5 stacks and popping something like Foresight or Shadowskin to make swapping easier (Shadowskin being the equivalent of being in Grit).