What about web-based apps which users can access in the browser without download? They can be very user-friendly. Big companies which do surveillance make their browser-based web apps crappy on purpose in order to coerce people into using their app-store app; precisely because it gives them more surveillance capabilities (e.g. location, file access, camera access, ...). A well-intentioned chat app does not need such permissions so a web app is a good medium.
I don't know if that's the case now, but not many years back Safari on iPhone wouldn't let you subscribe and receive push notifications. Even something as simple as that is enough to render a web based messenger useless. There's also no API to synchronize your contacts, which is something a 'normal' user would expect, nevermind rather awkard mobile browser tab management which confuses even me, someone who is intimately familiar with how web browsers work.
