It wasn't that Amigas couldn't do MIDI, Atari STs had MIDI ports built in and Notator software (the Killer Music App) is what made it the popular choice. The software on the Atari ends up being Cubase today. The music apps on the Amiga were more focussed on MODs rather than MIDI.
And yeah, the high school I went to rocked where it came to computers. 386s when they just came out, a room (yes a ROOM!) of Amigas and a couple Ataris in the music labs. I spent my lunch breaks playing games in the Amiga room though lol. They even upgraded to Amiga 3000s when they came out including a digitiser!