I mostly agree with everything you say, except for one thing.

I’m pretty sure it’s technically possible to detect nude images, on device, 100% securely, without anyone ever knowing it was detected. This probably isn’t the approach that some corporations will take, but as far as I am aware, this is how the current nude detection on iPhone works. It’s all on device, and just blurs it so the user has to accept a warning before seeing the content. If you control your phone, you can disable it. If it’s a phone setup for a child, the child cannot disable it. It’s up to the parent to specify what the child is allowed to do.