On the surface this post appears to be saying something relevant but a lot of it doesn’t follow. I would say that, in my experience, design is done for screen size and then a smart company will test their users most popular devices/browsers to ensure they work. When people say “mobile first” all they want to do is to remind people to actually design for a smaller screen rather than just transforming the desktop layout into a great big column of elements.
You have tendency to make assumptions about how people prefer to use devices based on what your own preference is. This is very generalised. Also you start off by looking at what facebook are doing — they are on a whole other level compared to most digital business. Facebook also has purpose built mobile apps…so you have quite the confirmation bias: throughout your whole article you focus on finding large screen examples.
They key point should be that we do design for screen sizes, but for now business can’t ignore the nuances of different devices when it comes to building the application — and the focus should be on what devices your users most prefer when it comes to testing.
Businesses should listen to their users and analyse their data — actions based on users and data will take a business from strength to strength. Business should spend more time on their data and act on it by building better experiences for their users.