I'd say both. If I'm a user who's all in on the Apple ecosystem, it seems like a nice plus that the out of the box apps can be expected to look similar and work

I'd say both. If I'm a user who's all in on the Apple ecosystem, it seems like a nice plus that the out of the box apps can be expected to look similar and work similarly, whether I'm on my phone or my laptop. There's certainly ways to screw that up, I won't deny that. But I think it's an inherently good direction to aim for. In my mind, that means (1) making sure that functionality is synced whenever possible (the lack of iMessage functionality on macOS after it was enhanced on iOS has bugged me for years), and (2) matching the look and feel to make the macOS version (or iOS version) feel familiar the first time you use the app if you've previously used the alternate platform's equivalent.