Darko was taken over 13 years ago. I don't see how the comparison even fits.
Just because Darko was European and a 7 footer?
Darko was skilled guy who just simply wasn't athletic enough to maximize that skill. He also didn't have the right mentality to become a "superstar." He could have been a very solid role player on the right team, and he wasn't drafted by that team.
We have to think of Bender in a similar way. From what I can see the kid has plenty of skill. He also looks to be fairly athletic for a young guy at 7 feet. Those are very good qualities to have in a top-5 draft pick. The question is: will be be allowed to develop into the appropriate type of NBA player he can be, and does he have the mindset to maximize his ability?
I can say without question that if Danny drafts him, the answer to the first part of that question is a resounding
YES. There have been very few, if any, draft picks during his tenure that failed to develop under Doc or Brad Stevens. The only one I can really think of is Gerald Green, and he wasn't here for that long any way.
But Danny, Brad, or the team have no ability to affect Bender the person. If he is not mentally or emotionally capable of becoming and NBA pro and working to maximize his talents, he will be a failure. This is true of every draft pick, but it has to be the primary concern when you are drafting 18 year olds who have little-to-no playing time to evaluate.