Speed of light as a fundamental constant

The Speed of light is considered both an invariant with respect to all observers (inertial or not). Indeed it is a constant of nature as light as an electromagnetic wave is notionally seen to travel through vaccuum with a constant speed. That vaccuum is a Platonic abstract empty space. Real space free of what we would call luminescent matter (5% of all matter in the universe) is a seething see of energy-matter cretion-annihilation. As such itwould seem to have some qualities that we attribute to a dielectric. That we define the speeed from Maxwell's equations through the permeability and permitivity of a dielelectric is testament to the fact that the electro-magnetic fields are the primary objects. As such should it not be the case that the mu and epsilon are the fundamentals of nature?