I can imagine a scenario when it's really useful, when portability is concerned. This segment right now is served by web apps, which essentially give the same end result, supposing a working internet connection: the user can have the same software and the same files on multiple systems, like a phone, and a PC. The device itself being portable would be the same, but infinitely more private: all the apps and files could live locally. Now, I don't know how large that market is, and I suspect that it's not that large, given that people are just fine with cloud based solutions.

In another words, I think that the functionality itself is very useful. It's just that it's currently being served somewhat adequately by cloud based solutions. For this reason, such a phone-pc product could not offer much in terms of functionality, and so, it might not be popular at all.

I don't think we can fairly compare a phone pretending to be a desktop against other desktops.

It would be more fair to compare a phone that has desktop features, to a phone that doesn't have desktop features.

So let's compare the best Apple phone that refuses to have a dex like experience; to a Samsung that has had a dex experience for about 10 years, or to a Google phone that is now adopting desktop experiences.

If the future is anything like the past, in 5 to 10 years from now we'll see a desktop experience on iPhone and they're going to be snobby about it.