Even the super slow ones like on kindle, are _choices_ that have been made in favor of something else. a second to turn a page on a book isn't unbearable
High-end Android phones have 120+ ms latecy. That's easily noticeable and actually annoying (at least to me).
My personal pet peeve is the latency of input when i'm starting new applications in KDE. E.g. I'll start a new terminal with Super+Enter, followed by a Super+Right Arrow in order to tile it to the right. But the latency is big enough, that often it's not the terminal that ends up tiled, but the application that had focus earlier, e.g. a web browser. It's really annoying.
I also don't understand how still in 2020 when I move a window with the mouse, the window can't keep up with the mouse.
30ms input lag is what we should work towards. But that's not what we have today. Today is actually crap.
I keep meaning to try out WindowMaker again as my Fedora window manager. I feel like it would be incredibly speedy on today's hardware.