I try my best to be right but not tight!
Alternative metal is a throwaway description, alternative anything means nothing! If one has to apply that to a band then that means the music is bad or at least has crappy genre aspirations (then again that kind of does go for anything that is already nu metal!)! I would be fine with calling System of a Down "freak metal" if it came down to it, ultimately the label is not important...but I think System of a Down was clearly related to the nu metal movement, particularly because the typical worst excesses of the other bands of that genre are the same mistakes they kept making.
Honestly bands like Linkin Park were pure pop/extremely bad rap, where on the other hand bands like Disturbed or Korn really had nothing but "playing fast and acting tough", I wish there a good definition to say "this is crappy and not metal and not hard rock and not pop, it is just a muddled shitty diluted mess birthed from the "noise war" distortion obsession that birthed us beauties like Metallica - St. Anger", basically "noisy rock" would work for me because it was basically generally simply an awful byproduct of the noise wars