But the style of his exit -- 19 years, not 20, no farewell tour, after a playoff year when he was a healthy spectator, despite a regular season where he was as useful as ever -- doesn't really detract from his legacy. 5-time NBA champion, possibly the best power forward in the history of the league, and quite possibly the best choice you could make to start a franchise with, in terms of career value, and how much guys wanted to play with him.
How good was he? Borderline unstoppable in his prime, with a game that was all angles, anticipation, and intellect. That signature bank shot, so retro it was nearly revolutionary for its era. Extraordinary defense, with length and anticipation that might have been the best of his generation. About the only thing that you could say negatively about him is that he was boring (winning is boring?), or that he whined for calls from the ref (unlike, um, everyone in his generation).
The single most spectacular thing about Duncan? His back of the bench ego and willingness to work with his franchise to ensure that they were always in the conversation to win a title. From deferring to David Robinson early in his tenure, to the first among equals nature of the Parker/Ginobili heyday, to the gradual transition to elder statesman and role model for Kawhi Leonard and LaMarcus Aldridge, there was never a question of whether Duncan was going to do right by the Spurs.
In an era where athletes seem to be defined as much by their endorsements, merchandise and post-game soundbites as they were by their game, Duncan was Just Game. The fact that the game didn't seem to change very much was an illusion, because the Spurs went from winning slow to winning fast, from championships in a grind and slug era to championships in the draw and kick era.
During his career, there's a very short list of guys who can be mentioned in his class. Kobe Bryant, who hurt his teams frequently, either through poor shot selection and teammate work, but equal in competitive fire. Shaquille O'Neal, who was kind enough to not be as serious about the game, thereby preventing the NBA from enduring a 10-year-run as constant champion. If you gave Duncan's mind to Shaq's body, basketball would have ended as a competitive enterprise. Kevin Garnett, never as skilled offensively, never as good in the playoffs, equally committed to winning and versatile in his prime, but a cheap punk out of it. And that's about it.
Extending the comparison to guys before and after his era, you take Michael Jordan over him, because he's just more fun to watch and better at maximizing his opportunities. You take LeBron James over him, because he's never worked with teammates as deep or as good as what Duncan worked with. Maybe you also dock him a few points because he only ever works with one coach, and that coach was also the best of his generation, and worked hard to keep him as useful as possible for as long as possible with minutes management... but if you've got a superstar with Duncan's production but none of the ego, your coach looks really smart for a really long time.
Duncan leaves the Spurs well-stocked, with Aldridge as good of a modern counterpart as we have in the game. He'll pass from the game like a ghost, with only Spurs Fan really selling out for his all-time standing. And we'll spend the next couple of decades hearing how flashier and younger guys should rank higher than him, because he more or less played his entire career in a quest to be as underrated as possible. And it's not as if he's going to spend the rest of his days staying in the public eye, a la Charles Barkley or O'Neal, to keep reminding us of how good he was.
But man alive, he was good. As good as anyone who ever played. And there was never another player who gave his franchise more.