AI Core Worlds Too Frequent

I'm playing as the purple Ewoks Miwot and have noticed my nearest neighbors, The Navigators, have decided that far too many of their worlds should be Core Worlds. Even a Class 11 world—Diadem II—that's surrounded by other Navigator Core Worlds, as seen in the screenshot below.

This is diluting the AI's military production, which essentially means I can rush-colonize several star systems while they struggle to build even a single Tiny ship.