Your points re Yehudi Menuhin are MOST valid, However, my statement about most steel players should have read (Steel Players that I know)
Surely being a musician involves the ability to recognise and DESCRIBE chord progressions and be 'au fait' with the usage of scalic phraseology.
I make no apologies that I would categorically state that in my opinion, without a sound knowledge of music and musical theory, one is only an instrumentalist.
Whilst most dictionaries describe a musician thusly:-
A musician is a person who performs or writes music. Musicians can be classified by their roles in creating or performing music: * An instrumentalist plays a musical instrument. * A singer (or vocalist) uses his or her voice as an instrument. ...
Just imagine this conversation about a specific lick. "You know the lick John Hughey plays at the beginning of the middle 8 of ??? well what inversion of the tonic is that?"
No.1. That conversation MAY occur betwixt a teacher and student, between accomplished players, I think not.
Most accomplished players would know.
Does NOT knowing makes them inferior ?,
NO, but it does make them less knowledgeable and therefore less capable.
In the world of Jazz where improvisational expertise is the main yardstick, the best men in that realm are mini composers. In many definitions of "musician" the use of the phraseology "artist who composes or conducts music as a profession" is a revealing judgemental standard.
So its patently obvious that reading or writing music also plays a part in the description, not to the exclusion of the other requisite traits, but as an extension of the descriptive term.
I know that reading is only part of it, and we oft make jokes about drummers, intimating that they are not musicians and they just hang around musicians.. Well. a few drummers I know have SIGHT READING skills that are phenomenal.
Johnny Wadham could read the morning paper whilst playing on a session and reading the dots simultaneously..Likewise Noel Kelehan.. Now THEY ARE musicians, not because of their nonchalant approach,(Which is naughty somewhat)
But inclusive knowledge of their instrument and its place within the overall genre's of music would be foremost in their mindset.
As you know, I am an AMATEUR etymologist and collect dictionaries and encyclopaedia, I have a litmus test that I apply to dictionaries, the word "wayzgoose" (well known in Margate or Blackpool and Fleet Street) if it's not in, then I don't bother with that particular dictionary.
Similarly I have an even more acid test for "Musician" besides the obvious, i.e. dexterity and diligence etc. I pose the question describe the usage of the half diminished chord, and instance it.
This is only for my own personal edification and enlightenment and to allow me to see inside the player's mind.
Again I simply MUST stress, it's only MY WAY to help ME assess capabilities..
I am not making a 'carte blanche' statement to the world in general,
just to myself as to whether I consider a specific player a musician, maybe my interpretation of the word is too strict, it's just my own assessment and description based on a semi educated insight.

QED Cogito ergo sum..