I am not sure I would categorize them as echo chambers (Fox being the exception) but their agenda is certainly not to represent the truth. They sensationalize and craft narratives, usually by lying through omission, or not covering stories at all. A recent example, Google "Steven Donziger CNN" and you will notice that there isn't a single story about him from the network even though his case is one of the most newsworthy of the decade.
You can have multiple echo chambers. Just because they’re different doesn’t mean they’re not all echoing garbage from their biased view points.
Fox News is the echo chamber of the right, while everything else is either extremely left or mostly left echo chambers. CNN, NBC, NPR, ABC,CBS spew just as much trash, however it fits the politics of the left.
It’s all biased, it’s all garbage. The only different is the politics of that channel.
