Things like this can't be undone, any more than selling off public lands.

The public lands is a bit harder, but this? This you absolutely can undo. Tell the license holders to sell off stations or they won't get renewals. Failing that, have the DoJ do its actual job and sue under antitrust regulations, then actually enforce a penalty where the broadcaster is broken up.

You can undo a lot of the damage, you just have to actually do it. We need to stop seeing these people as a group of participants in polite society, because they're not.