I completely disagree..
While it's obviously easier to play and learn the game when you grow up with it and are taught at a young age, it's still definitely possible to develop better fundamentals with hard work and studying IMO, I don't see how you can dispute that..
Carter's defense was fine when he put his mind to it, he was a good defender when he tried, even in college(key game vs. Rip Hamilton comes to mind, IIRC), which has little to do with fundamentals, and more to do with effort..this was a pretty common opinion at the time..his defensive effort has always been questionable..
It should also be noted that while Bryant is obviously a much better defender, he also had much less offensive responsibility on his team, at the time, and Phil Jackson himself has said that Kobe was overrated defensively..Kobe's game has also benefited greatly from Phil Jackson's coaching, which he himself has said..
I don't disagree with Vince being soft, he clearly is, but it was more from a physical and effort standpoint IMO..particularly a low pain threshold and poor shot selection, falling in love with the 3, which was never shaken out of him..he was a different player from a mental standpoint, stepping up in the playoffs when his team needed him(particularly vs. Philly in 2001), which wasn't the case as his career unfolded..
In regards to Kobe's fundamentals, he has clearly "improved" them, so I disagree with your feelings that you can't improve them..living in NY and all, I remember plenty of talk around the "Jordan vs. Kobe" ASG where Kobe was being talked about as having "more flash than fundamentals" by analysts and the media..while this doesn't mean he didn't have the proper fundamentals at the time, it's clear that they have improved with time, as he is now regarded as having one of the top 3-5 best fundamental skill-sets in NBA history..
Also, while Kobe's fundamentals were clearly better, Carter's physical advantages had him beat by a pretty good margin, especially pre-injuries..there's a reason many people took Carter over him at the time, and there's a reason they finished with similar results in MVP/All-NBA voting and were compared at the time(those accolades aren't my argument, obviously MVP and all-NBA voting are tricky, but the fact that they were close obviously shows that they were comparable for a reason)..