I'm not sure why people are worried about Sabonis and O'Quinn. Sabonis may be solid, but he works better with the second unit especially with the great pick and roll chemistry between him and Tyreke (no team would even dare start him in the first unit). If anything, Sabonis at worst will limit Turner's ceiling, which will make Turner at worst a upper-middle round pick (around 5th-6th round).
As for O'Quinn, well, he was more of a role player with above average stats by playing for the depleted Knicks. However, he'll have stiff competition with Sabonis. Also, Turner has much more to offer as a player especially with his shooting ability and range, and Turner does have some defensive skills.
When you pick up Myles Turner, you should know what you are getting. I got him at the fourth round for the blocks, relatively safe efficiency (except for foul trouble ofc), and capable scoring. Also, Myles Turner never struck me as a dominant rebounder (he reminded me of Serge Ibaka without the coaches and managers who force him to do everything at once) especially when people took notice of him for his shooting and blocking during his rookie season. If people are worried about rebounding, that's actually a category that is relatively easy to fill up as there are a lot of players below his ADP who are great rebounders. Plus, Myles Turner is a more of a finesse type of center, so you can definitely get creative with him in your line-ups while most of centers are relatively one dimensional like DeAndre Jordan or Dwight Howard. Also, waivers can sometimes have a good amount of rebound specialists, as big men tend to get injured more easily than their smaller counterparts.
Also, finally, with his Turner's skill set and his role as the second option for the rising Pacers, Turner has the ideal environment to make a comeback for this season. I cannot say if Turner has the champion's mentality like Oladipo; however, he shows the right attitude that will make him a future star (I mean if you want huge disappointment, then we can talk about Andrew Wiggins all day!).
Yeah, he was disappointing last season, but I think there's a very strong chance that he will at least be worth his ADP.