Hitting 40% of your 3s in the NBA on a reasonable sample size is HARD. I don't care if they are corner 3s or how the other team is defending you. Very few players do it. You can't say someone is a bad shooter if they pull that off.
Osman reminds me a little of Delly in terms of his long distance shooting. Delly's threes didn't look great, he had a little hitch and it took him too long to get them off, but he was really pretty accurate. In the early years with Lebron you could say that's because he was being left open, but he's also hitting 37% with the Bucks now. Of course Cedi is far more skilled than Delly in terms of his all around scoring abilities.
One area where Cedi could improve is in terms of getting respect from the refs. He is getting only 2 free throw attempts per 36, but getting whistled for 4.4 fouls/36. Basically, whenever there is contact they call it on him. If he can learn how NBA refs function while keeping all of his defensive aggressiveness, that right there will be a major improvement.
Once he irons out some rookie kinks and gets fully comfortable Cedi is already just about what we thought we were getting with Crowder -- an aggressive, physical defender who can hit open threes and score opportunistically. And that is as a rookie. I see him as a solid backup for Lebron and solid role player going forward.