Competition for spots isn't a bad thing. Gives the guy a break from the superhugemassive pressure of performing badly in the AFL, which lets face it, this thread has been popping all week due to his form at that level. He'll find his form and he'll be back.
As for Brown replacing him... well Brown is playing well in the VFL, McKernan is already in the side, and there really aren't that many KPFs left short of swinging Hooker forward (which they didn't do for some reason

). I'd say he probably brings some experience and maturity to the forward line as well, although probably not too different from Stewart given his injury history.