What's particularly puzzling about the formulation of "mainstream media" is that Fox is the most watched of the network news channels, and has been for more than a decade, and 15 of the 20 most watched cable news shows are on Fox:
https://www.adweek.com/tvnewser/january-2018-ratings-fox-news-is-now-cable-newss-most-watched-network-for-16-straight-years/356285
The formulation of anything non-Fox on TV as "mainstream" is factually incorrect, and as good a piece of evidence as any that this conservative formulation exists to merely allow the language of victimhood to permeate conservative thought.