Here's the way I might see this dilemma. Jefferson adds a tougher low post scoring threat than Boozer. Teams will have to put their biggest best defender on Jefferson all the time. Jefferson is way more physical and nasty than Boozer. Jefferson will wear him down in short order making him easier to guard for Memo, Fes, Jefferson, Millsap, etc.
Well, how many teams actually had problems with Jefferson playing center for Minnesota? Did the Lakers? Did the Jazz even?
And so Bynum will guard Jefferson. Gasol on Millsap. How's that going to be a problem for LA?
Jefferson can guard Bynum or Gasol. But can Sap guard either of Bynum or Gasol? How's that going to work out for the Jazz?
I'd phrase it this way: A shot-blocking center was more urgent with Boozer last year. But, especially against the Lakers, it remains an urgent need.A big shot blocking center may not be as urgent as it was with Boozer on the floor last year.
Getting a shot-blocking center means that the Jazz actually get somebody tall who can help against LA's bigs and serve as last-ditch defense vs Kobe and cutting wings.
Jefferson's fine as C in stretches but if he's supposed to spend most of his time there, that's just OK for a lotto team like Minny. As the Lakers are the team to beat, for a team like the Jazz that would actually want to 'contend', he'd be better maximized at PF as he'd be good-sized in that position ... so the Jazz need that shot-blocking center.