Everyone cites Rodman's superior rebounding over Duncan, but actually where it counts the most, the playoffs, Duncan outrebounded Rodman.
Even when you adjust for per 36, the rebounding is almost the same, which basically means Rodman's main fortay, rebounding, went down in the playoffs, while Duncan's has always gone up.
You have to go back a long way to find a player that rebounded more than Duncan in the 03 finals or had more blocks per game.
Again, the number one job of an NBA "big" defensively, is rim protection. Duncan blocked over 5 shots a game in 03, and almost 3 a game for 170 playoff games.
Not one GM would have taken Rodman over Duncan, even if you ignore Duncan's offensively prowess. Elite 7' foot dominant bigs are just too rare.
Chicago would have traded Rodman for Duncan in a second had they played at the same time....