Classical music is the height of technicality but it's also at its best the most amazing music, not just musically but artistically, the spirit of it. I don't think you can compare metal and classical except that they're composed similarly and have a similar spirit. Even classical guitar is improvised a billion times better than the best rock, jazz and progressive have to offer.
But metal is non-trivial to create and to play. For how simple it is, it isn't predictable like rock, and there are many subtleties that your average musician cannot accomplish. Dave Matthews playing Beherit would be a laugh-fest.