This is the whole thing with Dragan Bender. He doesn't have any real major flaws, but he doesn't have any real major stand-out talents either. The biggest selling point is the fact that he is only 18 years old, and so you hope he can surprise us all and take his game to a whole other level. That's a big risk though. He may well just develop into a pretty good all round player who isn't great at anything.
I think it's very unlikely Bender will be a complete bust. He should (at the very least) be a quality starting center in the NBA for many years. I just question his upside - does he really have the talent to develop into a big star? I'm not so sure.
This is where bringing a player in and getting into his head matters. If he has an elite motor, bbiq, and work ethic, he can be as valuable as Kawhi Leonard. If he doesn't, he could be a bust. If Bender is strong in those areas, i would take him over a big man with prototypical size and elite athleticism who is questionable between the ears.
Kawhi Leonard is really not comparable to Bender though.
Leonard always had a ridiculous wingspan for the SF spot, outstanding athleticism, excellent physical strength, and excellent mental toughness (with a 'never back down' attitude).
Guys who have those attributes tend to become outstanding defensive players, but Bender lacks in a few of those areas. He greatly lacks physical strength, his wingspan is actually only good (rather than amazing) at the PF spot, and he doesn't seem to have a lot of mental toughness. Even if his motor and work ethic are high, he still looks like somebody who could be easily pushed around - something you cannot say about Leonard ever.
Before somebody questions my comment about his length it's worth noting that Bender is 7'1" with a 7'2" wingspan. Jared Sullinger is only 6'9" and has a 7'1" wingspan. Bender certainly doesn't have a disadvantage in terms of wingspan, but he doesn't have the type of advantage a lot of people seem to think he has. Dwight Howard for example is only 6'10" and yet he has a 7'5" wingspan. Lemarcus Aldridge is 6'11" and has a 7'5" wingspan. Pau Gasol is 7'0" and has a 7'5" wingspan. Tim Duncan is 7'0" and has a 7'5" wingspan. Zach Randolph is 6'9" and has a 7'5" wingspan. From memory Dirk also has a wingspan in the 7'5" range.
There are a lot of big men in this league who are a lot longer then Bender is, and there are certainly a lot of big men who are a lot stronger then Bender is, so unless he can prove he has superior skill (which I'm not seeing at this point) he might well struggle to score and defend against elite NBA bigs.
Simmons has the same problem as far as length goes (even moreso, in fact) but he can somewhat make up for that with elite physical strength, elite athleticism and a rediculous array of skills.
People compare Bender to Porzingis, but Poirzingis is 7'3"+ with a 7'6" wingspan and is already a very skilled shooter and a very capable scorer. Bender lacks that major physical advantage, and looks less skilled (although he is two years younger then Porzingis too).