The team is probably already playing Jefferson too much, which brings us back to Corbin. Here's a remarkable thing: Utah's five most-used lineups this season have been outscored. Ditto for 17 of its 18 most commonly used three-man groups, and usually by margins much larger than Utah's overall negative scoring margin.
Only two of the 80 teams that have qualified for the playoffs in the last five years have done so with their top five lineups being outscored: the 2008-09 Bulls, and … last year's Jazz. This is very strong evidence that Corbin is basically just playing the wrong guys and wrong combinations in the wrong minutes distribution. His better defenders and all-around guys — Favors, Kanter, DeMarre Carroll, Gordon Hayward, et al. — deserve a larger chunk of the time going to Jefferson, Mo Williams (now back from injury), and others. Lineup data can be pretty noisy over short sample sizes, but the noise is getting really loud at this point.
There's also the fact that Utah's defense plays with a weird lack of discipline and unclear, unproductive rules. That's partly on Corbin. Jefferson and Millsap are both slow, but Corbin's de facto strategy for defending the high pick-and-roll — the play that kills the Jazz5 — is to have the big man defending the screener jump out so that his body is positioned perpendicular to the baseline, as Jefferson does here in failing to prevent Brandon Jennings from turning the corner: