Except that doing a task started on your phone that you can continue on your ipad pro is not something that one can do with Dex. I do admit the one big use case for a desktop and it can be done via an HDMI adapter, is answering emails that require a long response, using keyboard and mouse.Eh? Or you just unplug and carry on with what you were doing on the phone.
One of the things that with tech that sometimes occurs is a narrow use case is made to seem like a general use case and for the masses, which is one reason why "objectivity is really hard".
Dex is a good example of this...and I agree it's a tool on the tool-belt and sounds great in theory, but if I am going to be tied to a monitor to do work, I'm using windows and that is my opinion. (Although playing games on your phone to your monitor sounds like a good use case)
I'm lucky enough to have friends that let me "play" with their devices. I'm definitely an iphone person as for my use case ios just works better. I always thought using Samsung that it's a collection of "features" and not a real user experience and you sort of corroborated that with a few tech items that don't seem to add much to make the more expensive Samsung devices best sellers.