Oh, I remember that. That was because all specs had access to the wonderful first version of ISF. Awesome talent. But then ISF was moved further down in Destruction tree, and the other specs that lost it remained in -12% damage state. Lovely hotfix.
And mutual CD on both demon forms is weak. In case the tank dies when we are in Meta, it prevents the glorious role of "Thrall's balls, we are all going to die" tanks. Makes sense. At least it will prevent strong defensive on demand in PvP.
And 30 sec Soul Swap... What is the actual GCD benefit of that? Especially with DoTs having duration of around 30 seconds if clipped anyway. And is BoA still 1 target only? Because that would demolish the Soul Swap.