"Finally having a voice assistant app confirms the suspicion I had when Siri arrived on iOS: I don't really have much of a use case for this."

I definitely can relate to this. I only have three real use cases for Siri these days - setting an alarm, starting a timer and setting a reminder for myself. All three work pretty well with Siri.

I just don't use it for much else. I don't use Siri's dictation features because Siri only shines at dictation when you know exactly what you're going to say, word for word - for "casual dictation", it falls apart really quickly. I can't think of anything else that my first reaction is "let's ask Siri".

Cortana feels like a really expensive "me too" feature.