There is a lot more to multiple monitors than that. Desktop icon behavior, doesn't stay where it belongs, especially if you have a mix of icons on various desktops, or don't have your icons on the primary display but DO have the start menu on the primary display, but not on the secondary display. It goes on and on and on and on and is mostly the ENTIRE FRACKING REASON why there are three or four intensely dedicated programs specifically intended to fix the things that should already work in Windows, but don't, like Display fusion, Ultramon, Actual multiple monitors, Dual monitor tools, etc. So, yeah, it does not work correctly, and it NEVER has. Anybody who says otherwise, has clearly not tried to go beyond the most basic of configurations with two, three or four monitors, especially if there is a mix of resolutions, refresh rates or orientations.
I can appreciate that you believe it works fine, but I assure you, it doesn't. There are many ways in which multi monitor support in Windows could, and should, be vastly improved. And for what it's worth, I've been working with systems since before there WERE any Windows versions, so this is definitely not a case of the rodeo vets snickering when the greenhorn shows up.