Samsung's Dex Turns the Galaxy S8 into a PC
techradar.com
techradar.com
The hardware is certainly powerful, with 4GB RAM and a fast processor. I remember using a Windows 3.1 machine with a 25Mhz processor and 8MB RAM. If that can drive a usable GUI, smartphones certainly can.
A phone as PC is one less device to research, buy, configure, maintain and upgrade. It's one less chance to get your data out of sync, or leave it stranded on the wrong device. It's also cheaper than buying a desktop or laptop.
It's not right to say that one form factor does a better job for all use cases.