I think that one could make a case McDonough has fanned on too many early draft picks although the final determination will not be made for years to come.
Here are some draft results:
Len was drafted #5.
Dragan Bender was drafted #4
Marquese Chriss was drafted for the Suns at #8
And Josh Jackson was drafted #4
This can be contrasted with some other early draft picks who were very successful in more recent NBA history.
Amare was drafted #9
Shawn Marion was drafted #9
And Joe Johnson was drafted #10 by Boston
Of course the Suns hit on notable later picks.
Booker was drafted at #13
Nash was drafted at #15
One could make the case the Suns would be better off drafting #9 or later.
As PFKK eluded to, an aspect that often goes missing when discussing draft prowess by a GM is "Who else should they have drafted?" Said differently, "Who'd they miss out on?" It's also very helpful looking at redrafts to gain perspective. (In parenthesis I put a rough estimate on Gain vs Loss on redraft)
2013 Draft:
There are 2 legit stars after Len (Greak Freak and Gobert). Lots of solid players. Len probably gets redrafted in the high teens (18?) after his spike in rebound stats this year. (-14)
2014 Draft:
Hood and Jokic were taken after Warren. Outside of that, no one better. Warren gets redrafted at 10. (+3)
2015 Draft:
Booker is a lock top 3 pick. No one is better than him after #13. (+10)
2016 Draft:
Really tough to do a redraft a year removed.
Bender would still go top 10.
Chriss's arrow pointing down, but he's still extremely young. He's probably still redrafted top 10.
(+0 on both)
2017 Draft:
Josh might not be lighting it up but he looks the part of an athletic raw talent. Would still be a top 3 pick, although Lauri, Kuzma, and Smith are making pushes (Ball and Fultz are out)
(+0)
In all, McD gets a roughly estimated -1 on his picks. (This number should be used to compare against other GM's +/-)
He missed out on Greak Freak and Gobert, but that's it. Not bad for 5 drafts.
He got one star in Booker.
He has ZERO busts.