2. Bradley Beal
It might be a surprise to find Beal here, because you could make the argument he is actually an underrated defender. He is still lightning quick and gets back in transition really well, while also managing to stay in front of his man most of the time on any given night. Even better, he won't always have to guard the best perimeter player on an opposing team.
Both Booker and Durant will take turns at that - although Durant may have to be moved into the middle because of the aforementioned Nurkic issue - meaning Beal can be hidden on the best shooter from deep that an opponent has for example. Underneath all of that positivity though, which should rightly be given to Beal, there exists a more ugly reality.
Beal continues to get hurt this season, and giving his all on the defensive end isn't going to help him stay on the court when the Suns need him. So the solution is either to try less hard defensively, or else risk being unable to play in a series altogether because of injury. Neither reality is what the Suns signed up for when they traded for the 30-year-old.
An opponent like the L.A. Clippers could force the Suns to put Beal on James Harden, while the Nuggets could throw Michael Porter Jr. his way a lot in a series as well. If that sounds overly negative, do remember that these are the teams the Suns are going to have to go through if they plan on winning a championship. Which is still the primary objective here.