I don’t understand those people at all. If my browser window is the width of a mobile phone’s screen, than a version of the website designed for that size is exactly what I want!
Right! If you've got a window that narrow, the only way the design will even work or layout correctly is with the "mobile" layout...
The bigger problem is people hiding functionality if you're in the mobile breakpoint. That's an issue: all functionality should be enabled, at least in some way IMO. Mobile should never be a second class citizen :)
There's also a big problem where the mobile layout will tend to make controls huge to present a reasonable size touch target. This is unnecessary on the desktop, and may even result in less information fitting on screen than before switching to the mobile layout.
That allows the dev to select for devices that do not have a mouse and such rely on touch targets, to increase the sizing. I've been implementing this myself recently in our web application, while still allowing us to change the layout to fit the narrow width!
I'm sure there are some devices it doesn't fit perfectly for though. This stuff is capital-H hard.
The implementations for these have some... complications, the device sets we now deal with are huge, and making sure there are no idiosyncratic bugs that creep up when using them is legitimately a fair bit of work.
> If my browser window is the width of a mobile phone’s screen
It's not, is the thing.
I have a 23 inch screen for my 1080p screen. My phone has a 6ish inch diagonal.
When I make a window 960 x 1080, that's still something like 10 inches across and 11 inches tall. It's sheet-of-paper sized. I'm perfectly comfortable reading that as it was designed for a desktop layout.
I would say that half of my monitor, more accurately, is about the dimensions of an iPad at comfortable viewing distance.
Phones are far taller than half of a 1080p screen.
Half a monitor is: 960 x 1080, or 1:1.125
A iPhone is: 828 x 1792, or 1:2.164
So websites tend to shove a candybar shape into a nearly square sheet of paper and waste a lot of usable proportions for things like controls or hamburger menus.
Not necessarily: the real-world size matters too. Desktop-sized UI is hard to hit on a touchscreen when shrunk; meanwhile mobile-sized UI wastes space when enlarged on a desktop monitor.
