Having worked on an app that, at least in my opinion, was pretty well done for each platform (phone and iPad), this is the case. Our UI for the iPad was a comp

Having worked on an app that, at least in my opinion, was pretty well done for each platform (phone and iPad), this is the case. Our UI for the iPad was a completely separate one. The core code was shared via various internal libraries, but the UI was entirely different. Adding a feature to iPhone required one entirely separate set of code compared to the iPad app. The app was a universal binary though and one app ran on both device types. This was, at the time, an absolute requirement. There was no way to scale the app from iPad to iPhone in such a way that it would give a great experience on both iPhone and iPad. It just wasn't possible to give an excellent app. I've long since left and the app does seem to be written in SwiftUI now and seems to be one shared codebase. But I wouldn't say it's as good as it was previously.