JavaSound has worked pretty well for over 10 years when the direct device support was added. That’s a generally solid low level API. I wouldn’t recommend most people use it directly, like I wouldn’t recommend most people on here use PortAudio directly, which is the low level library used in OpenAL-Soft. Likewise you wouldn’t criticise PortAudio for not being as easy to use as OpenAL. Julian assumes that JavaSound based libraries are hard to use because JavaSound itself is.
Or another way, it’s similar to what you said about it being possible to build JavaFX on top of LWJGL.