isolate. The ball would stop with him and if he ever did pass he wouldn't continue with the set - he'd generally just stand and watch the other 4 do their thing. He's a great player but he has is own thoughts about how he should best be used, and a flowing read-and-react system isn't it.
I didn't watch much Suns this season, so this observation may be off-base, but it can be very tough to implement a cohesive system, whether we're talking offense or defense, if your superstars aren't driving the effort. If they'd rather do their own thing there's going to be a limit as what that team can accomplish. Booker seems more willing to buy-in, but I'm sure Suns fans will have a better sense. As good as he is, I think there's a reason why KD has only won with the Warriors. This might sound nuts, but if I'm Phoenix I might just trade KD for serious pieces to fit around Booker and Beal.