Yes, I considered added something similar to what you said to my post. But you failed to take in account one thing: if there were no vocals, the music would be -completely- different. They would never have made these songs with repeating riffs every single song with no vocals. And without all those screams, a lot of the transitions would completely lose the impact they use to have (just think about the first times you heard Mask of Sanity and Taste of My Scythe for example). See what I mean? I mean, what would Needled 24/7 be without vocals? I probably wouldn't like it. But then again if they were an instrumental band that song would've never existed. I hope you see what I mean.
Despite what a lot of ppl say about vocals in metal, without them, metal wouldn't be metal. It's part of the whole attitude and aggression. Even better example: what would the song Hate Crew Deathroll be without Alexi laying down the law? It'd still be intense but I don't think it could ever compare.