I know the reasoning of that statement but it's not providing an argument to refute. What am I supposed to say? "No. You can't, that's why it's not happening".
1) You can add websites as app icons to iOS and Android. 2) Websites can hold persistent identities, and devices can otherwise remember the login details. 3) Websites UI can be anything and have nearly all options that apps can have, depending on the quality of the UX, which depends on the designer in any case. 4) A professional website will not be any slower if properly designed.
Now on 5, that depends on the specifics of the app. Some types do benefit greatly from being boarded on a device. An example would be Procreate for instance, which can not be mimicked on par in webform.
2) Websites do that through Cookies and Local Storage. These have limits and users would be purging them en mass. The data of the app doesn't disappear for no reason.
3) As I said, the problem is that it runs within a browser if not added to the homescreen. It is a window within a window.
4) Professional or amateur design, websites data is managed by the browser and not you. Caches get invalidated, you download everything again. It happens all the time.
Just being able to do something is not enough, Apps are much smoother experience.
