alt Hacker NewsHence the caveat "Aside from the loading times," :)
The "instantly" refers to user input: clicking a button, typing, or moving the mouse was as fast as it could possibly get because of how close the OS was to the bare metal, with no fluff bogging down the experience. Simply put, there were no wasted frames, as there were none to waste. Nowadays, at the very least, you get a couple millisecond of latency. That was not the case here.
Also, this is a machine from NINETEEN EIGHTY F//G FIVE, and it's still probably faster than your average PC running Windows 11.
The GUI was fast because it was fixed layout, MUI on the Amiga was slow as well. We tend to go that way to get UI that is easy to create. You see the same in all GUI libraries the more CPU you have the more you use it.