Unfortunately this writer does not understand the boot loader security on iOS. Since Apple's signing key is burned into the device, Apple is the only one who can modify its functionality by loading new firmware. Even in that case, the only firmware that can be modified without unlocking the device is the lowest level boot loader, which likely has numerous size and functionality limitations, as all the device features probably are not enabled. I would not deem this a flaw in device design. If Apple creates a signed piece of software that allows for a brute force exploit, it is creating a backdoor for the FBI.
https://www.apple.com/business/docs/iOS_Security_Guide.pdf