I don’t think Turner could be classified as even an average rebounder. His highest rebound % is 13.9, and he’s currently sitting below 11 - Theis is sitting over 15 and was at 16 as a rookie.
For the discount Smart is in terms of contract, and for the intangibles and leadership he brings, I wouldn’t even consider a deal based around them.
I'd probably keep Smart too, but this idea that Turner is going to kill our rebounding when we've been playing Horford and Theis at center the last few years don't make much sense to me. 11 vs 15 or 16 is cherry picking - their career numbers are much closer than that, with Turner playing every night alongside Sabonis who is by far the best rebounder on either team while Theis was usually the best rebounder in his lineup.
PTS / REB / BLK / 3PT
--------------------------
13.6 / 6.7 / 1.3 / 1.1
13.3 / 7.2 / 2.7 / 1.0
That's Al Horford and Myles Turner last year, and Turner played slightly fewer minutes. Horford was the superior passer, but Turner had double the blocks, double the free throw attempts, more rebounds, and a higher 3PT%. This is not to say I would have preferred Turner last year, but I think it does shed some light on the level of criticism here and unwillingness to trade any valuable asset for him.