"The media" and "social media" may not be controlled by a single actor, but it's common knowledge that large enough chunks of both can be and often are.
For example, the conspiracy theory that Russia rigged the 2016 election for Trump is based on this premise.
There is also a widely-accepted partisan divide between the encumbent news sources on the left, and Fox and newer so-called "fringe" or "alt" news sources on the right. These in fact aren't correctly fringe or alt - at least in the US - as clearly very close to or more than half of the US population for the past decade has indicated they have political beliefs aligned with them.
It's therefore as disingenuous to attempt to delegitimize "alt right" media by referring to it thusly, just as it may br for right-leaning media to do the same by referring to the left as "fake news". With this example, both sides are behaving in uniform ways exactly typical of unified, single-actor control, respective to each.
If the Russian conspiracy is true, the premise that single-actor control is possible is accepted, as it therefore happened with enough force to alter a major an election. If it isn't, then half of the US is legitimately right-leaning, making the labelling of their mainstream news sources as "fringe" or "alt" or "extreme" indeed tantamount to "fake news".
Either way, it's mistaken to believe it impossible for the control of single actor to be enacted upon a large enough portion of the media to achieve widespread adoption of their agenda.
In effect, your last paragraph directly contradicts your first.