I mean, language is hard, and it evolves. What they called mediums, we now call (quantized) fields. QED would say the photon field _exists_ at all points in spa

I mean, language is hard, and it evolves. What they called mediums, we now call (quantized) fields. QED would say the photon field _exists_ at all points in space and that it is kinda fair to say that it is a "medium" for electromagnetic forces and waves to propagate (with the additional point that special relativity is required to understand how to correctly transform it into a different reference frame, rather than imagining it as a strictly Newtonian medium).