I think Safari support for PWAs is by now good enough that at least web apps added to the homescreen get to keep their local storage indefinitely. So that is an avenue for apps that can live with the restricted web environment.
Interesting! So does safari have different storage rules depending on where the web app is accessed from? Are there docs detailing what else might operate differently? I wonder how many web devs test their apps under the different constraints.
With PWAs the idea is that if the user explicitly "installs" them they get exceptions and better integration, yes. I don't have a reference at hand and don't know the details on iOS, but hopefully "PWA safari support" finds some clearer things.
That's still not guaranteed be indefinite, I have encountered it being cleared after iOS updates on numerous occasions.
I will add that I was pleasantly surprised at how easy it was to turn the web app I initially had into a mobile app with Ionic.