macOS does have weirdness with windows that span multiple screens. I bet some of that kicked in to an unacceptable level. It can create incoherent moving/snapping, for example. Has been kind of crazy-making for a while, for my set-up where screens are not joined but adjacent in a triangular configuration.

Yeah, that's something that was unambiguously better back in the "Classic MacOS" days (probably starting with the Mac II). Windows could overlap multiple screens and they were always drawn correctly.

At some point in OS X in the switch to hardware acceleration, they started rendering windows on one screen only.

I get that you hardly ever really want a window spanning two screens, but when you accidentally misplace a window it would be handy to be able to see it on each overlapping screen so you can track it down. Right now you can put a few pixels of the title bar on the wrong screen, and the rest of the window just vanishes.

These regressions are weird given that modern hardware is vastly more powerful than a Mac II.