Myles Turner's stats are not all that different than Theis' and Theis gets those stats in 6 minutes less per game. Given Turner's upgrade is so small as compared to Theis, I don't see sacrificing the heart and soul of this team, Marcus Smart, to try to get Turner.
Numbers never tell the full story. If anything, Smart is the epitome of this.
Much like Smart, Turner is a terrific defender. It's not something you see on the box score, but it makes a huge difference on the court. Not to mention, he spaces the floor, which means that Brown/Kemba/Tatum/Hayward would have more opportunities to thrive as slashers.
Theis spreads the floor and lanes are open for our guys all the time. He also is a tremendous defensive player where the stats don't tell the whole story.
Turner is just not that big an upgrade over Theis' and certainly isn't worth giving up Smart for that upgrade.
Theis is hitting 30.5% of his threes this season in 1.3 attempts per game. He ain't shooting many threes. More importantly, opposing defenders often dare him to shoot. On the other hand, Turner is hitting 34.9% of his threes in 4.3 attempts per game. Again, he ranks 2nd among all Centers in 3-point FGs made per game. Opposing defenders follow him on the perimeter, hence he creates space in the paint for his teammates. Brown would thrive as a slasher next to a guy like Turner.
No comparison in defense either. Turner is one of the best defensive Centers in the league. He defends the pick n roll, he defends the perimeter, he protects the rim, he can hold his own against traditional Centers, he can do it all.
If you ask me, Turner >>> Theis. It's not even close.