re: NuMetal is the most egregious assault on music since it's inception.

Yes I would say the main aspect of nu metal is the rap influence, which bands like Godsmack and Disturbed don't have. Some people just lump every band that came out around that time into nu metal but they don't all fit. Slipknot and Deftones had some rap influences on the first albums but moved away from it. Slipknot does still have a dj though. Nu metal is one of the more fluid metal subgenres, lots of bands may dabble in it for an album or two but then change it up later.