I may be wrong, but I think the point he was making was his general on-court demeanor which I would agree has regressed (but I also don't blame him a whole lot for).
Last year was a bit of a nothing year, the team didn't have any direction. Favors needing significant PT, while Jefferson is a lock to start.
This year we know that Gobert will be ready in 2 years time. So the FO can probably guarantee Millsap that he can start next to Favors over the next 2 years, with Kanter 3rd big off the bench. The certainty of a starting role should be much better for Millsap.
To get him to bite, we can sell him on the fact that in 2-3 years time we'll have a team that contends.