Look, there's a big difference between trusting known ciphers that have been well studied by the world's top cryptographers, and a proprietary TPM chip that relies on security-through-obscurity.
The history of embedding secrets into black boxes is a history of them being broken. This isn't a theoretical concern, it's a very practical one.
Physical defenses are not security through obscurity, and why you assuming they don't use known ciphers?
OTOH, the practical purpose of encryption is to remain unbroken for long enough, not to be completely unbreakable. As seen here, security-through-obscurity is practical enough in cases where user-obtained key material is too weak to provide enough protection using strong publicized crypto. In other words, it's a two-part key: one is in user's wetware, the other in phone's hardware (as per obXKCD, it's usually easier to attack the former).
I disagree. The pin validation is done within the secure enclave. You can't do it outside the secure enclave because the pin is combined with a secret that is burned into the silicon of it. The secure enclave can and will enforce timeouts for repeated failures, as well as refuse to process any pin entries after too many attempts. Disabling the wipes or bypassing the timer won't do you any good when you only have a few attempts.
https://blog.trailofbits.com/2016/02/17/apple-can-comply-wit...