UI usability: This is a discoverable, good UI: https://jbss.de/bilder/scr118d.gif . You can instantly tell what is a button, where you can enter text and what is inert. You can even read out all the hotkeys from the screenshot. Now, without hovering over it with your mouse, check the header of this post (the grey line) and tell me which strings will take you to a place (= are a link), which do an action (= are a button) or are inert. They all look the same and you need to investigate it first with the cursor. And even then you can't tell the buttons ("flag", "vouch") apart from the links ("parent", "context").

Latency and performance: I played RTS games for 15 years. Despite getting old and rustly, i easily hit 120 APM during office work. I can tell if an application can handle it. Things like the Windows Start menu were fast enough for me until like Vista, but now they aren't - i need to wait a bit or i click before it is popped up.

The CPU/GPU required to render an interface at 60hz has gone up inline with moore's law.