Ah, but the Atari didn't have the co-processors that the Amiga had, you could also program the sound and graphics chips and leave them doing their own thing and they'd interrupt so you could handle things like sprite collisions.
The ST was popular due to it's built in MIDI and the advent of cheap synths (and all that naff 80's electronic pop

), however on a technical design front, I think there's a lot to be said for the Amiga's design.
The 68000 was also used in Sinclair's QL, this again was another very powerful computer, however it's packaging like a fat spectrum didn't do it many favours.