I would call him out on it again, but say that you warned him, now his team will suffer the consequence. Tell him perhaps over the course of the season he will learn more because if he doesn't demonstrate some improvement he won't get the invite back.
I don't like having guys in my league who aren't learning and because of it are dropping players that are way too good to be dropped. For one, I don't want a team that is destined for the bottom of the standings because of their ineptitude, and for another I don't want something like waiver priority deciding a league.
Sure waivers help, but a #1 waiver priority isn't supposed to be the ticket to adding a proven star player. It's supposed to be about getting the guys that the deepest team in the league just can't quite afford to keep, but that are valuable to other teams. One man's trash is another man's treasure, but you can't have owners that are throwing away the core of their team like garbage.