Those incidental things are 99% scripted. I'm sure he does a little improv, but less than you're giving him credit for.I don't think you understood what I meant.
I meant that you get a better feel for Drake's character from the incidental things he says while climbing or fighting etc that North just comes up with on the fly. He comes across more human in these bits.
If you judge him by what he says and does in cutscenes, the character makes little sense. His motivations aren't convincing.