Part of what makes a player great is his ability to inspire and get the most out of his teammates, coaches, gm's etc.
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Some say my reasoning behind Duncan is flawed due to the gap in talent he had surrounding him versus the talent KG had surrounding him for the majority of his career. And I counter by saying Duncan's greatness enabled that surrounding cast to succeed and win 4 titles. Not the other way around.
But can't you see that this reason is inherently biased? As someone pointed out earlier in the thread, the David Robinson that Tim Duncan played his early years next to is a better player than KG has ever played with in his career. This had nothing to do with Duncan's ability to inspire, it had everything to do with a freak Robinson injury and the Spurs winning the draft lotto to pair one historic player with another.
On the other hand, you mention getting the most out of teammates. KG has done that just as much as Duncan has, if not more. Cassell earned the only All Star appearance of an almost 20-year career next to KG. Wally owes his All Star appearance to KG. Hudson owes his big contract to KG. KG always is among the league leaders in the +/- stats, indicating his teams tend to shine when he's on the court even if they suck elsewise.
The difference is, you can't get blood from a turnip. David Robinson was an All-Time great. Ginobili and Parker both would have been prized prospects if the rest of the league was as up on international scouting as the Spurs were at the time. Yes, I'm positive that playing next to Duncan inspired those players to heights they wouldn't have reached without him. But the thing is, you can't say that KG was less inspiring because he wasn't able to carry Wally, Hudson and Rasho Nesterovic to the same heights. In fact, I'd argue that KG getting a 50+ win season with a supporting cast like this is just as impressive in a "getting the most out of your teammates" sense as winning a title with Duncan's crew.
ETA: Fafnir just said the same thing as I did, but a lot more concisely.