Most people on desktops / laptops interact with these services via a web browser, which has very limited permissions on the system. Not sure how you could control that tightly on a fully open iOS.
It does, doesn't it? Even if you stretch "web app" to mean "PWA" iOS supports them. And it definitely supports the literal definition of "web app" (i.e. loading a website in a browser that runs JS or whatever to perform its "app" functionality).