More or less. Unity was an attempt to have the UI component of applications / apps so written that they would adjust to the display size and Human Input methods present at the time - I believe it started out during the netbook era ( 7" - 10" screens, mouse, keyboard).
Samsung only need to have a few key apps ( Pareto analysis, we use 20% of apps 80% of the time) such as browser and Office to adjust to big display mouse keyboard tlfor this to be viable for some users.
A few years back Apple took a different route: rather than plug your phone into a display you could continue working on the same document across iOS and OSX, with the document (and where in the document you were currently working) being zapped between phone and Mac over WiFi. However, the popularity of iOS over MacOS means that Apple are now giving developers tools and guidelines so that an iOS app can potentially present a decent user interface when run on a Mac.
I stated a few years back that my personal opinion about Ubunto and DeX (and whatever Microsoft called their efforts) like solutions was that by the time you've found a spare monitor, mouse, keyboard and carried cables around, you might as well carry a little headless ARM PC with you. After all, they're not pricey, give you reduncy should you lose your phone, and don't tie up your phone in cables (so you can telephone a colleague whilst looking at a spreadsheet).