Author!Anon (Don't worry, I know what you meant! You were tired!) Yup, definitely a dominance/control thing, he wants to prove he is in control here. You are completely right about being more kind to Newt, and if Grindelwald was planning on keeping Newt long term he would be doing that, but as it is he's not expecting Newt to survive. And he hasn't realised quite how attached Credence is.