To be frank, graphics world had some type of standard (OpenGL) long time ago, next to DirectX. So WebGL had a good example. However in the audio world we haven't seen a cross platform quasi-standard spec covering Mac, Linux and Windows. So IMHO, non-web audio lacks also common standards for mixing, sound engineering, music-making. That's why web audio appears to lack a use case. IMHO, that smells opportunity.
I use Web Audio, in canvas-WebGL based games where music making is needed. I understand the issues - we definitely need more than "play" functionality.