I also imagine Moyes is getting him up to speed with out of possession responsibilities etc too. Not an effort thing, but things like shape, pressing triggers, etc.
Out of his competition for the attacking line behind the striker, Illi has already had half a season with Moyes and Grealish and KDH are both seasoned pros used to playing under tactically demanding managers. Dibling has one season under a series of dreadful managers. Understandable if it takes him a few extra training sessions to understand everything he needs to do.