Before we go to comparing KG and Duncan (both GREAT in different ways). We have to also look at the help they had at that position.
It doesn't hurt that Duncan had Robinson at the beginning of his career (SOLID help) and other serviceable big men. Even now, Duncan has Splitter, who can at least spell him some minutes without the entire team falling off.
At this stage, KG shouldn't have to be heavily depended on and utilized in order to win a game. That's on management.