You have fundamentally misunderstood the interoperability that is being discussed re: podcasts and drawn a totally spurious conclusion.

You can connect to nearly any podcast using as little as an RSS reader. You can build your own podcast app TOMORROW and that app will be able to access pretty much any podcast from any network (with very narrow exceptions for the worst actors, e.g. Spotify exclusives, NPR One, etc).

The only purpose of the various platforms is boosting discovery. There's nothing oligarchic happening there; for pretty much all of them listing your podcast is free. There's also absolutely no necessity to use any particular platform's discovery tools or to list your podcast on any platform. It's totally fine to distribute it yourself, via a link, using whatever means pleases you. Your "podcast discovery platform" could well be your local bookclub's email list -- and while the quality of that discovery may be worse, it in no way inherently limits what you can access. Even if you use that platform's app, it should still generally be possible to add any podcast via RSS URL (if any major apps don't support this, they're behaving in a deviant way).

There is absolutely nothing oligarchic in general. At least for now, so long as the fucking fuck fucks at Spotify don't get their way.