MIDI is not "just an event/messaging protocol", although it could be used like that. MIDI describes an application-level schema for "channels" which allow for t

MIDI is not "just an event/messaging protocol", although it could be used like that. MIDI describes an application-level schema for "channels" which allow for the dynamic control of "notes" including pitch, poly after-touch, etc. It also provides for channel-level control parameters, various special application-level events. Global clock transport, bulk data transfer, etc. It's true that you could implement all of these with OSC, (indeed there is a standard embedding of the short MIDI messages into OSC), but OSC is in general silent on application-level semantics. This makes OSC a much better choice if you want to implement some other semantic, but you still need an application level schema for commercial music devices, and that doesn't exist.