Yes, this is the strongest argument against it and the biggest flaw. They keep saying in interviews that they are treating their future selves as adversaries and they do open source most everything but I would be a lot happier if the protocol development was spun off into a separate org from the for profit service. If it dies, this will be what killed it. But I hope they make it (by it I mean the tools for everyone else to make the ecosystem).
The freshrss GitHub has a list of supported iphone apps and indicates some of them work offline. https://github.com/FreshRSS/FreshRSS?tab=readme-ov-file#apis--native-apps