A mate of mine was a full time musician for a few years then he got a job but still does gigs etc by your definition he was a "true musician" but then lost the status.(How about someone who has retired are they no longer a true musician?).
I do not play an instrument I only sing but I have been paid, I do not think if you asked for a definition of a true singer that many people on this forum would say it was someone who was a professional. If you are trying to provoke a response- congratulations you succeded if you are really interested in what you posted start a thread the way bagpuss sugested. Cllr