Is it worth building an entire social media protocol just for the sake of Bitcoin?

Yes.

The more significant changes (inactivity reboot, USB controls, MTE, controlling JIT in Chrome, cellular network attack surface reduction) was already in GrapheneOS for a long time. It's still good to see the stock OS implement these features, although I wished they gave users more choice and control with it.

GrapheneOS has an edge in all of these features compared to the stock OS. The inactivity reboot happens earlier by default and can be configured to happen as early as minutes. The USB control is disabled via hardware for us and you can even disable charging when booted to OS. We implement MTE in far more than just apps. You can have a LTE only option rather than just disabling 2G.

The majority of the rest are Google service related and aren't in the scope for us. Users can use a Google service on GrapheneOS if they wanted.