Kassian's main problem is that he has to 'think' about every move on the ice. Not much of it comes instinctively. He needs time to process the play, and by the time he does and acts on it, the moment is over. Low hockey IQ.
Will/could he get better? I don't know except to say I'm waiting to see more. But I will admit that as each day passes, I think more that Darcy Regier shook Gillis down that day.