That Atari didn't do anything special. The MIDI went in/out of a standard interface and the interrupt was - IIRC - on the keyboard line. Midex was a step up, because the messages were pre-buffered, which was a little quicker. But MIDI timing was pretty bad anyway, because the serial line was too slow.

It was tolerable if you put every synth/drum machine on its own separate buffered line. But when you had four or five devices connected to a single MIDI out on the Atari - ha ha ha no.

The absolute best timing resolution was around 700us, which is fine for single notes - although that didn't allow time for the steam age 8-bit processor in the target synth to wake up and notice it was supposed to do something.

But when you had a four note chord, it never sounded truly tight. And if you added some aftertouch or mod wheel - oh dear.

So you ended up with this weird cultural thing of music that was quantised and on-the-grid but also had quite a bit of timing slop.

Big-name bands often used synchronisers and tracked each synth line to tape in a separate pass.

USB over MIDI is much better because there's basically zero latency and everything (usually) works as it should.