There are a few reasons I can think of to have an Android or iOS app for Stack Exchange:
- it allows for notifications on your phone
- it gives users that expect an app and search in the App Store something to find
- at minimum, an app is a convenient bookmark for the site
In practical use, the current Android app is strictly inferior to the mobile site in my experience. I'll just add a few issues here I remember running into:
- MathJax doesn't work in question lists or in comments
- you can't see deleted posts at all, even if you have the privilege
- the list of favorite sites for switching isn't synced from the list on the desktop site
I'm sure there are aspects that the app does better, but the last one I remember was the seamless login into all sites at once, but that issue has been fixed on the websites for a while now, so the app has no advantage here anymore. But I can't think of any features related to the actual browsing and asking/answering/editing experience that would be infeasible to implement in a mobile website.
The one killer feature of the apps are the notifications, there are quite a few heavy users of SE that find those useful from what I observed. So my suggestion would be to focus the apps on the part that isn't easily possible with a mobile website.
For me, the current restrictions of the Android app are annoying enough that I pretty much always use the mobile site, even though I have the app installed for the notifications. The ideal app for me would provide notifications, but simply redirect to the mobile website when I follow them.
There's still enough stuff in the mobile site that could be added or improved. Instead of splitting the efforts between the Android app, the iOS app and the mobile website, focusing on the website alone for the core SE usage should take less effort.