Oh Jose, Jose, Jose you trouble maker you
Tiago is doing
exactly what the Spurs want and demand of him. You know that if he started trying to do too much, Pop would plop his butt on the bench and he wouldn't see playing time until the next season.
When you say
"you're forgetting the past few times where Pop went with set up ball and picked Dice/Diaw over Blair." the key word there is few, those times are getting fewer and further between.
The Spurs offensive system doesn't require or need a guy who can simply pounds the ball on the floor while he backs down to within a foot of the hoop, because that causes the offense to come to a screeching halt.
Would it be nice if he were the second coming of David Robinson or Wilt? Sure, if this were 15 years ago. Everyone admits, he's a better passer, he adds more to the Spurs overall play than Diaw, Bonner or Blair, because if he didn't he wouldn't be starting and playing as many minutes as he does.
If you want to bring Jefferson in, then do it to replace Tim because that's going to be the biggest hole to fill in the near future.