Duncan led the league in FGM, 2PGM, FTM, Defensive rebounds and total rebounds, offensive winshares (10.7, 0.5 over the 2nd best in the league), total win shares (17.8, 4.2 > 2nd), box score plus minus (7.6, 0.6 > 2nd) and VORP (8.1, 1.1 > 2nd).
Led the playoffs in blocks per game at 4.3 blocks, putting up 27.6ppg and 14.4rpg. He also led the playoffs in BPM that year. That year was better, numbers-wise, than the best seasons of Nowitzki, Barkley, Erving, Malone, and Larry Bird.
If you want to talk how he didn't go past the 2nd round, in the series vs. the Lakers, he put up 29/17.2/4.6/1/3.2 vs. 21.4/12.2/3.2/0.6/3.0 for Shaq, and 26.2/5.4/4.8/1.0/0.2 for Kobe. If you do the math, both Shaq and Kobe, supposedly two of the top three player in the NBA, put up a TOTAL of 47.6/17.6/8.0/1.6/3.2 for the entire series. Duncan put up similar rebounding and block numbers by HIMSELF. So yeah, it was dominant.
The only compe ion for him that year was Shaq, but Shaq was coasting and didn't play a full season, so the award rightfully went to Duncan.