Also add to the fact that I could be trained to play 2 or 3 Bach or Beethoven tunes in less than a day, but it would probably take 2-3 months, perhaps years to play Metallica, Queensryche, Kansas or Rush . The degree of complexity is like comparing a balsa airplane to the space shuttle.
My oldest daughter will sit at the piano and play some truely great classical pieces (she's getting pretty good at the sight reading thing)... then, she goes in her room, down tunes the guitar and proceeds to play the darkest riffs.
Personally, I think her classical piano training is paying off, making her a better metal player, but that's just a personal opinion.
Sometimes, we sit together and crank our amps, and play riffs from March Slav... Downtunes, with distortion, and annoy my wife - another music snob who hates metal. Heh heh.