i think they are both in play here. but one thing sticks out about Magic to me. in 12 seasons, he went to 9 NBA Finals. and while Bird began to decline from injuries, Magic started winning MVPs and still went to the finals a couple times (even as Kareem turned 40, declined to simply being a slightly above average center, and finally retired). the extra couple peak years from Magic make all the difference. may be unfair to Bird, because injuries aren't his fault. but that is the way their careers played out. sure, Magic had great teams, but so did Bird. if anything, i think that's why Duncan belongs in the conversation with them. because while, yes, he didn't beat opponents as great as they battled, he did win his titles with significantly less supporting talent around him.
in any case, all three of them are perfect examples of how superstars can create an entire culture that leads to success. the coaches and organization are important. but the leadership has to come from the star player to make it work. this to me is the biggest difference between Duncan/Bird/Magic (at least, the older, more mature Magic) as compared to Wilt/Kobe/Shaq. all six great talents. but the first three had more consistent success because they created an environment where every member of the team had to rise to their best and they utilized every teammate in the best way possible. the second three had seasons where they were completely unstoppable, but all three had several teams that simply exploded or underperformed because of leadership/chemistry issues.
Regarding the team argument. Yes, Duncan played on less 'talented' teams...but the team itself was still always good (by virtue of coaching, i'd think). so, hat i'm saying is a good player on a talented but dysfunctional team is still, well, playing on a shitty team. If you can attribute that lack of function to a lack of leadership, then it's an argument that diminishes the player in question's greatness. But otherwise, is that really such a good argument? I thin in the case of kobe, shaq and wilt it applies. but on the flipside, with duncan, idk.