the fact of the matter is, Millsap (and Harris for that matter) is gonna be going downhill by the time talent has accumulated enough to be in the playoffs... getting younger, bigger, and faster is the best thing we can do right now.
While I agree with you in part, veteran leadership and work ethic is needing among young guys. Millsap epitomizes this more than anyone on our roster, in addition to the fact that he doesn't take anyone's spot and would fit within a dynamic where you have something like Favors and Kanter up front. Jefferson, however, wouldn't fit in assuming Favors and Kanter are solid starters. He also wouldn't fill as strong leadership role as Millsap, in my opinion.
I'd be ok with picking up Knight if they really feel good about him. The fact of the matter is that as a freshman he put up some pretty unbelievable numbers. However, if you think he's a just a solid player ala Devin Harris caliber, then I think you may as well just pick up a guy like Jimmer or Jackson and have more ball handling run through someone like Hayward and let Kanter and Favors play inside while kicking out to guys on the perimeter to bomb threes (like the Robinson/Duncan Spurs -- not equating Favors or Kanter to either of them but you get the idea). But if you think his ceiling is higher than someone like Harris then you look to make this move.
But then again, what's this source, again?