If you want to have a cross-platform experience (mobile + web), you'd have to have a server component.

We do transcript, chapter and summary extraction on the server (they are reused across customers), RSS fetching is optimized (so we don't hit the hosts from all the clients independently), our playlists are server-side (so they can be shared across platforms). As we build out the app, features like push notifications will require a server component too.

I agree with you that a podcast app can be built entirely client-side, but that will be limiting for more advanced and/or expensive use cases (like using LLMs).