The whole thing relies on hardware security modules, so even if you can prove that the whole software stack is working as described, there is literally no way to know that the SE isn’t secretly handing the OS keys that a third party can decrypt.

There needs to be trust at some level, and trust in Apple the entity to not be outright lying about its thoroughly documented security posture is a reasonable level of trust for most people on the planet, including those who are at very real risk of targeted attack by state-level actors.