No, ALSA also does the mixing (dmix) and provides lots of plugins in libalsa. PA tries to fix the problems in those parts of ALSA, problems that should not exist to begin with. PA exists because of problems in ALSA.ALSA is for the drivers and PulseAudio does the mixing, filtering, routing and so on.
Again, the focus is "problems in ALSA." There shouldn't be any.
That doesn't make it right.From developers perspective ALSA doesn't matter as they either target GStreamer, OpenAL, Phonon... or PulseAudio directly because it's the de facto audio server on Linux.