"The model should never become the application's security boundary" is the line worth anchoring on, typed output and guided generation improve reliability, but neither substitutes for the app independently validating ownership, permissions, and business state. Structured output is a formatting guarantee, not an authorization one.
The Android vs. iOS framing as "modular vs. integrated" rather than "which model is better" is the right lens, AppFunctions being explicitly labeled experimental preview while Apple's Tool protocol ships as a stable native API is a real asymmetry teams should weigh before betting production architecture on either.