The chart below shows how many matches were scheduled from 1995 to 2010 between the two Western Australian teams, the West Coast Eagles and the Fremantle Dockers, compared to the Eagles versus the Brisbane Lions.
In sixteen years, the Eagles and Dockers played against each other 50% more often than the Eagles and Lions. If the Dockers were weak during that period and the Lions strong then that is a good outcome for the Eagles, but not for overall fairness in the competition. It's certainly a long enough period for all pairings to be scheduled evenly.