I guess?
Neither of those things are dead though (news is struggling with the adblocking apocalypse, but that's a different category of problem). I kind of get what you're saying, and I agree that Facebook and Google are powerful, and that we should look for ways to distribute that power more evenly.
But at the same time, to me those scenarios kind of look like distributed architectures doing the jobs they're supposed to. I mean, Google Reader's shutdown hurt bloggers less than Live Journal's did, right?
Another way of looking at it: think about what happened when Microsoft bought Github. A bunch of people panicked, but for the most part, it was fine - because Git repos are decentralized. And a bunch of people came out with hot takes that said, "Git's not really decentralized, because Github is the part that matters."
But... no, for the most part it's decentralized, and we saw the benefits of that architecture.
If you have a decentralized core you might interface with or feed off of a few centralized services, but you will be more resilient and better equipped to deal with their failures. You don't have to be perfect to reap most of those benefits.
If iTunes stopped distributing podcasts, that market would suffer. But I'd still be able to directly share episodes on Twitter and Reddit, and there are at least 2 other preloaded sources on my listening app that could be serving the same purpose within a day with zero change to the way I find new podcasts or download them. The big change for people like me would be that when searching, I would click the second button on a list of sources instead of the first one. It would definitely hurt the health of the network (mostly just for iPhone users), and you can make an argument that it would disproportionately hurt the health of the network, but it probably wouldn't kill it.
But suppose Apple or Google stopped distributing an app store. That market would instantly die, for basically everyone, and no one would be able to do anything to save it.