Did OP really just call Slipknot "super hardcore"? It's every 10 year old prepubescent kid's idea of extreme metal, who haven't really heard actual metal or any subgenres.
Besides that, lyrics DO matter, because I don't know about other intelligent people, but I like intelligent lyrics. People on the radio with lyrics that don't make sense or are like this;
"You had left me a week ago
We were too young, what did I know?
Too old to need, too young to care
Now I wish I'd stayed with you there
OOOHHH BOOO HOOO OHHHH BOOO HOOO
YA WA DIPPIDY DOO
OOOOOHHH BOOO HOOOO OHHH BOOO HOOO"
Yeah, that proves that they don't deserve to be on the radio over anyone else, because ANYONE could've came up with shit lyrics like that. Say what you need to say in a unique way from everyone else. That's what makes a great song from a shit generic song. Think about it from a new perspective. Use different imagery and metaphors and stuff. Mess with the structure to reflect the song, ect. Makes it more interesting and uncopyable.