You are correct that FSF does not consider the entire system at large as free. AOSP and WebKit are certainly really free in the FSF sense, but sure, almost all Android distributions in practice also contains some non-free software in addition to the free stuff, critically the firmware blobs for radio and other chipset drivers. In principle, you can get a fully free Android to browse the web over WiFi if you have an appropriate hardware; the code for all parts of the stack to do so is available. Things like GrapheneOS come close. Most users can install a fully free browser inside regular Android too (same on iOS, Windows, Mac and desktop Linux). Realistically, the biggest hurdle in the user freedom for Android is not the non-free software, but the devices employing signature verification in hardware/bootloader (i.e. Tivoization).