I think the thing that some people overlook is how irreplaceable Ray Allen is. Now that's not even to say that he's better than Vince Carter (though I think he is). But Ray Allen meshes with Pierce and Garnett in a way that most other big stars couldn't.
I read this argument a lot when people make Ray Allen trade ideas. How do you know another superstar could not sacrifice their game to win a championship? I thought the Lakers team did it nicely the year they got Karl Malone and Payton. The reason they did not win a championship was not chemistry, it was the fact Malone seriously injured his knee.
That's only a small part of it. The Pistons still won in 5 games. Malone injury or not, there were still another 3 Hall of Famers on that team. That's no excuse to lose to a team with arguably NO Hall of Famers.
One of the big problems with that Lakers team is exactly my point. It's not just about sacrifice, it's about how well your games meld together. Malone actually worked out well. While he doesn't quite have KG range, he can drift out and knock down the 16-18 footer. Had he not been able to do that, he and Shaq would have had a hard time coexisting in the post and Bryant and Payton's driving lanes would have been shut down.
Payton, on the other hand, was a horrible fit. And that doesn't necessarily have anything to do with his willingness to fit in. As you know, the triangle offense Jackson runs is not run through the PG. Thus, it's most successful with PGs who are great spot up shooters. Payton didn't fit this mode at all and struggled mightily to fit in. This is why he averaged a career low 36% shooting from the field that season (25% from behind the arc) despite having more open looks than anytime in his career. This is also why in the Finals Derek Fisher put up better numbers than Payton did in the Finals despite playing less minutes: Fisher could hit the trey, Payton couldn't. And it wasn't only just that Fisher was a better shooter: Fisher was used to hanging out around the three point line waiting for kickouts; Payton wasn't. Thus, Payton's already mediocre three point shooting became worse.
This is why I say Ray Allen is so irreplaceable. Even if another star wants to fit in (which is a gamble to begin with), his game will have to mesh with the other two. And as I just showed above, it's not just about looking at stats. Carter is historically a good three point shooter. But can he adjust to becoming less involved with the offense and becoming a spot up shooter? I'm not so sure.