Encryption is useless if there is a way to brute force crack passwords or acquire private keys which could be used to decrypt a device. In most ways, yes, physical access is 'game over for security, so I could see Cook & co. make the case that these devices are so dangerous in that regard that they shouldn't be able to be used by anyone.

Tl;dr It's covering your butt when Apple can say to the FBI, 'We support your efforts and want to help you, but literally cannot because it would require dismantling our own security architecture.' No engineer would agree to that - they would quit in protest.

The NRA crack is more about them being the GOP's puppeteer. Under a competent (and probably Democratic administration), being labeled a domestic terror organization would kill their funding in 0.02s.