Duncan is a great great player but his legacy is a little overrated because he has played in San Antonio with Popovich for his entire career. He has a great organization, a great GM, a great coach, Great supporting talent and a great system. He has been essentially a part time player for quite a while and they experience almost no drop off when he isn't on the floor. He's averaging 8.5 points per game right now and he's only scored over 15 per game one time since 2009-10 season.
He could end up with 6 rings or more and he's won an ungodly shit-ton of games in his career but no way in hell is he better than Wilt, MJ (pre Wizards), Kobe(pre achilles tear) or Shaq (pre getting fat). He just doesn't have that kind of dominant impact on games by himself. His statistical averages are about the same as Pau Gasol. He's a system player, very skilled, very smart, very efficient, very consistent, very good in the locker room. He's a guy anyone wants on their team but people are chiseling his name on Mount Rushmore and it's a little absurd.