Interesting discussion. To restate the original question, "If one learns to sing/play correctly, will that person lose some of their personal signature?"Hell no, but I'm using my own definition of 'correctly' when I say that.
In our area there is a vocal teacher who has a lot of students, and has a good understanding of vocal technique, harmony and technique. But just one problem: has lousy pitch. Some of this teacher's students develop into very good singers, but I hear a lot of off-key kids who have been taking singing lessons...(we got to a lot of school concerts and the like).
I'm not usually the strict parent, but I put my foot down when my daughter wanted to study voice with this person (everyone she knew was doing it). For several years. Recently (finally), a friend who is a singer-songwriter--and who knows how to deliver a song with both precision and feeling--was finally able to start teaching my daughter. It's going well, and I'm glad I waited for the right person to be available.
W-O