To be fair, not really. Yes, we did not have full control over Grimm, but from my point of view, because we as player it's cript what was writen by TCO or Leaf. Like a IA if we talking rude way. Creator give to us some value of informations, and power. We have a script what to do, and yes, even if we can sometimes do something different, it's still all part of plot what was writen by someone who above us. But in game, was enough moments, where exactly Grimm take control. Even was fully fallen, he still have his own though and desire. In last moment, where we run away, we as plot can choose whatever we want, but Grimm really love Red Hood, and he did not want to let her die, so his, HIS choice was cut own hand and fall in hugs of TCO. Maybe even if Grimm it's slave, he still have his own mind and he can sometimes ignore plot and just do what he really want?