I believe that you left out an important component........ physical ability..... some people have the coordination, mental capacity, and physical attributes that are special.
ironically, I was just thinking about this last night.... what sets the greatest of all time apart from the others ?.......
For singers - I believe it's that special voice.... there are a million great singers ( which I'm certainly not one of! ).... but there's only one Pavarotti, Elvis, Johnny Cash, Barbara Streisand, Frank Sinatra, Rod Stewart, Freddy Mercury, Bob Marley, Bob Dylan, Roy Orbison, John Lennon. Ray Charles and Aretha Franklin. ( And I know there are more!)
These are the voices that you don't need to look on the screen to see who's singing...instant recognition because of their unique sound.
The same goes for guitarists....... there are loads of great guitarists, but the ones that had the ability to make that guitar sing in a special and unique way, they are the ones that stand apart from the others.
Very similar to greatest Athletes of all time - same criteria.
I also believe that emotion/ personality / charisma comes into play - while I was very, very impressed with this young lady's performance - I thought it was emotionally deprived. I love the musicians that exhibit passion and excitement for that the song they are playing or singing, and show that it really means something to them. Hers came off as a musician that practiced and practiced, nailed the mechanics beautifully... but lacked the heart and soul of the music. Just my opinion.
Thanks for the thought provoking thread - I'm sure it will get some responses.
Your vision is not limited by what your eye can see, but what your mind can imagine.
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"Use the talents you possess, for the woods would be very silent if no birds sang except only the the best." - Henry Van Dyke