Interesting observations to be sure. Though I think there are MANY
degrees beyond advanced intermediate. Music, IMHO is rather like
martial arts where black belt is recognized as expert and can be
achieved by many with hard work.
Mastery of the techniques and a firm understanding of how the music
works are the beginning of the expert spectrum. (Notice I did not say
you needed a music degree or that you necessarily need to know the
formal names for how to express your musical ideas.) Next we set our
sights on (a) life long growth and (b) being unique. I make no claims
to uniqueness but the "a" element of the equation is what keeps me
going. That's my .02.