If you add the PWA to the home screen from say Chrome then Chrome should run the PWA. If you uninstall Chrome then the app is removed from the home screen.
How do you ensure that it works? does chrome have all the hooks needed to have this actually work correctly?
A third party browser should be able to do the same things as Apple's browser. Same for all apps: they should have access to the same features of the device as Apple's apps.
Apple's rationale in their letter about this was essentially that they would need to ensure that it works (create and review use of a framework for non-Safari-backed PWAs in iOS) and that (usage of PWAs) x (percent of userbase affected) was too small for them to bother.
...or the next time you run that PWA, you should decide between running it with another browser or deleting it.