Amlogic hardware is hardcoded (in silicon) to search for bootable firmware on eMMC, so unless eMMC is erased or electrically disabled to prevent u-boot from being found; the boot rom finds it and runs it. The toopick method applies to vendor u-boot, the (Android) recovery mode scripts are not implemented in upstream u-boot.
I fixed this on my own board by resoldering dry joints on the UART connector. Another user shorted a pin. It's also possible to short eMMC pins to disable it allowing SD boot to the box image and then restore the factory image. I totally understand that not everyone would be comfortable with those options, but from a pure "is it recoverable or not?" perspective, it's recoverable.