Aminu wouldn't be that much of an asset at the 3--his three-point shooting isn't consistently good enough when compared to other wings. What gives him value is adding some spacing from the 4 while being able to defend most 4s. That type of player is what every team is trying to find. Aminu isn't amazing at it, but he's capable. Honestly, if Collins were ready for it, the ideal alignment would be Collins at the 5 and Aminu at the 4 and <player to be determined> at the 3 (if Harkless had just continued his play from last year, he'd have fit in relatively nicely at the 3). A stretch 5, a stretch 4 and a three-and-D wing at the 3 is the ideal alignment these days.
Nurkic is an out-dated center--that still could have worked if he were actually as good as he looked last season after the trade, but now that he's regressed to career norms, he's the kind of center that's slowly becoming extinct.
I don't think Stotts is a great coach; average, as Nik dubbed him, sums it up. But the Aminu hand-wringing is way overdone and isn't remotely an issue that makes Stotts a problematic coach. That's one of the things he's doing right.