No doubt Kobe has been better from 2008 to now, but even over a career, what Duncan accomplished from 1999 to 2005, Kobe has done nothing remotely even close to that level of accomplishment.
Kobe was given a team of weak supporting cast, and he missed the playoff once and got ousted in the 1st round twice. Duncan got a weak supporting cast from 1999 to 2004, and he got ousted in the first round once because he didn't play in it, and then got 50+ win seasons, WCSFs, and even a ring during that time.
People forgot how crap that Spurs team was in 2000 to 2004 without Duncan, because they won a championship and have the name SJax, Tony Parker and Manu Ginobili in 2003 and 2004, but really look into that team, watch the games they played. David Robinson, clearly way over the hill at that point, was undoubtedly the 2nd best player on that team. Robinson, at that point in his career, wasn't anything close to a Pau Gasol of 2008 to 2010, or even a Pau Gasol of today, he wasn't even at Bynum's level today, and he was by far the 2nd best player on that team.