Question: if the OS does proper app sandboxing how is this basically any different from having unrestricted access to a web browser or email?

Oh no granny tapped a bad Google ad and got phished! I guess we should kill the open web and use the officially sanctioned “web store” from now on (where you have to apply, pay a fee, and of course a % commission to host a website). It’s much safer for us!

It is not funny, but this already happens. ID verification mandated in some countries already take care for that under disguise for children protection.