Genuinely curious, why is that better than just having good midi i/o? I would think almost anyone doing composition and notation, who has expensive, realistic o

Genuinely curious, why is that better than just having good midi i/o? I would think almost anyone doing composition and notation, who has expensive, realistic orchestral libraries to play things back on, already has a DAW of some type. And the type of full control you're describing sounds like it could really include a lot. You'd need features like a recording timeline and playback control, parameter automation, advanced routing options, return tracks, side chain inputs, plugin latency compensation, ability to freeze or record plugin output to save cpu resources. Pretty much everything a daw has.