For some reason, folks are bound and determined to think of players as similar to parts on a machine; interchangeable. Any time you get a chance to upgrade parts, of course you do it, and to decide whether it's a good idea or not, it's always assumed to be just a matter of running the numbers.
But see, I DON'T ever want the NBA to be like the NFL. I don't want the players to be treated like machine parts - and even in the NFL it doesn't quite work out that way all the time (cf Doug Flutie vs Rob Johnson).
Sure, if you just totally discount the human factor, Duncan over KG is a nobrainer. But KG has been the heart of our team for four years, the man more responsible than anyone else for reviving Celtic Pride. How do you even entertain the thought of switching him out. How can one possibly assume that Duncan would have had that same effect? Something almost miraculous happened here in Celtics Land.
So would the seventies Celtics have been a better team if we had McAdoo instead of Cowens?
What about Wilt instead of Russell? No one would take such questions seriously for a moment.