For me it wasn't so much the per-app/stream mixer but per-stream dynamic routing that was the important feature of Pulse (though I've moved on to PW now). I'm

For me it wasn't so much the per-app/stream mixer but per-stream dynamic routing that was the important feature of Pulse (though I've moved on to PW now). I'm not too sure how this is handled on other platforms, but pre-PA the in-app volume control would often modify the global mixer, rather than implement an in-app mixer/attenuator, which is definitely not what you usually want. In most Linux apps these days, those controls manipulate and are synchronized with the PA mixer, so there's still only one actual mixer, they are the same control. I assume that other OSes also do per-stream mixing in a similar manner, and just choose not to expose the mixer for whatever reason. As much as people complain about PulseAudio it's always worked well for me, and from what I've seen of Windows and macOS alternatives, it's more featureful and usable out of the box.