The problem is not with ActivityPub, but the implementations. No one ever claimed that it should be only a push-based system, but it seems that everyone working on AP software can only think in terms of server-to-server interactions to get the data and then reinvent the wheel by developing their ad-hoc API.

AP is fine if we treat it as a messaging protocol and use it to power offline-first applications. The devices do not need to have all the network's data, just the one that the user has actively interacted with.