Entirely agreed with your analysis, but if we extend it out a little bit I think there's still a couple of issues here (if we assume my presumptions below are true) if we sign Željko.
Presumption 1: Most likely we're going to have to field a pretty similar roster.
Presumption 2: This C's roster doesn't look like the best team to run his preferred way of playing basketball.
1) The roster is largely out of his control in a way that it won't have been with Fenerbahçe (Euro teams tend to rebuild much more year on year than NBA teams do), so really we have to see how much of the roster is an Ainge creation and how much input Stevens actually had.
If your coach has a system that works well with a certain type of player and your organisation doesn't manage to stock your roster with those kind of players, it can be a hard road. Looking at the roster now, it doesn't look like the best team to hand over to a guy who wants to play in a particular way.
2) The style of play in the NBA is more open, generally. the closest Int'l league is probably the CBA.
Secondly, the talent disparity in the NBA is also more on display. All of these guys are world-class basketball players.
Off the top of my head, the best guys that Željko has coached are... Bojan & Bogdan Bogdanovic, Jason Thompson, Nemanja Bjelica, and Ekpe Udoh? Systems work better at lower levels of competition (see the NCAA), and they don't always translate when you have to play against the absolute best in the world.
Now, having said all of that, the style of play is absolutely gorgeous and I would be thrilled if we managed to land him. I just think it might be a bumpy road