Your statement about manually turning off the Safari features is wrong.

iPhones have and have had since the first iPhone, the ability to add a website to the homescreen.

You, as the developer, need to include META tags referencing icons, status bar style etc. We are still trying to decide if Safari is using the web manifest or not for this.

But a homescreen web app will launch in full screen if you set these values correctly.

In fact at that point the only real difference between a PWA on the iPhone homescreen and a native app is not needing 6-10 app store steps to install the exact same thing. Plus the business does not need to worried about arbitrary Apple guidelines and censorship.