Since joining a real team (like Duncan's Spurs), KG is 4-3 against Duncan and averaging 17 PPG, 8 RPG, 2 APG.
Duncan had Robinson next to him in those early years and then he had Parker, Manu and Co. in the seasons after...
I'm not saying that Duncan isn't one of the greatest big men of all time, but it's not like those SAS vs MIN match-ups were just Duncan vs. KG.