"""There should only be one API. Top layers should be things like GTK, OpenGL, Motif, stuff like that. Third-party low-level APIs like Xserver should not exist. The existence of Xserver is proof of Linux's failure in graphics."""
A audio server performs a similar function to the display server. It provides a intelligent way to manage audio I/O and multiple applications.
I suffered through using Alsa for years. I did many advanced things like setup custom configurations to multiplex audio inputs and all sorts of junk like that. And I can tell you from experience that Linux audio is shit without Pulseaudio.
There is little proof needed beyond then the continued misunderstanding and misrepresentation of Pulseaudio show that there is still a large segment of the Linux user community that are not interested the least in understanding the technology of the software they are using and just run off of little more then emotionally fueled ignorance.
Every once and a while I run into something intelligent somebody says that shows that PA sucks in some way, but that's rare nowadays.