To my mind, the goal is not to have an exact sound replica of the metal song; the goal is to play the metal song the way it would sound if it had been written for the classical instruments and in that style, not the metal style and not in an imitation of the metal stule.
Still, kudoes to the people who do this. They are amazing!
As an aside--Chamber Maid--a Baroque tribute to Tool barely sounds Baroque in most of it. There's quite a lot of Middle Eastern drumming, and one song sounds almost as if it could have been written by Barry Manilow. There is one song on the album that has a lovely harpsichord bit, and the song "Aenema" sounds quite nice on this album. The rest of them, though...Meh.