I guess it depends on if you think System Of A Down was a nu metal band since they were still pretty big throughout the decade. I don't think they are despite some nu metal type riffs. The music and lyrics were much more advanced than Nu-Metal. Like musically they were borrowing riffs from Black Metal bands like Emperor even. The lyrics also had so much more heart and importance behind them compared to:
[Verse 1]
It's a fucked up world and a fucked up place
Everybody's judged by their fucked up face
Fucked up dreams, fucked up life
A fucked up kid with a fucked up knife
Fucked up moms and fucked up dads
It's a fucked up a cop with a fucked up badge
Fucked up job with fucked up pay
And a fucked up boss, this a fucked up day
Fucked up press with fucked up lies
While Lethal's in the back with the fucked up eyes