It's not always about right vs left. The point Doyle is making is that Fox has lost its edge in sensationalism and outrage, which was a big part of its draw.

At this point it isn't really clear how right wing the Fox News audience was to begin with. Certainly Trump didn't win on anything resembling a conservative platform. This isn't to say that the loss of O'Reilly and Kelly didn't Fox's ratings, but that factor is unlikely to have been the cause of the ratings spikes that CNN and MSNBC have been enjoying.