The stupidity of this argument could be boiled down to the government trying to file an antitrust lawsuit on the Rolling Stones having an ongoing monopoly on rock music because movie directors are still deciding to use their superiorly popular (and in my opinion superiorly written) music over all the modern hacks.

I dont think this is an issue of antitrust, rather an issue of regulation.

You regulate the internal affairs of the oil industry not because you still care about the monopoly Standard Oil once hand on the market, but rather because you care about how they can directly operate in such a way that has been proven to cause more harm than good. (e.g. this is why california is so up tight about getting your car "smogged")

There is a debate that needs to be had regarding how the power of big tech flies in the face of the 1st amendment when it comes to how internal bias can harm the public in the same sense that somebody yelling "fire" in a crowded theater can cause trouble.

But this doesn't fall under antitrust and I think distracting the real issue with this kind of lawsuit is just another way for Washington to feint like they are "actively" trying to do something about the problem while in reality allowing for the problem to persist into the long term future.