There is clearly a use case for keeping the whole UI. But it is the major use case and should the whole product philosophy be based on it ?

I feel there will be more sites where the URL won't matter or where the user will prefer simplicity to control.

I use Google Maps 99.99% in PWA mode and never mourned the lack of the URl bar, especially as I can open the site in normal browser mode anytime I ever want the full controls.