It doesn't quite work that way. The files on the device are ultimately encrypted with a dependency on both the hardware key in the Secure Enclave and the user's passcode. It's impossible to update the firmware without both pieces of information or erasing the device, and on A7 or later processors the unlock attempt delay is a direct result of the method of encryption used and tied to the hardware so it must be performed on the device itself.
https://www.apple.com/business/docs/iOS_Security_Guide.pdf