By hardcore I meant hardcore punk, not like post-hardcore. I was referring to how most people say thrash metal is a combination of a New Wave of British Heavy Metal and hardcore punk, especially with Metallica. Then you look at bands like Slayer, and you can see where the speed, black, and doom metal influences start to show.
On topic, I can kind of deal with deathcore better than metalcore. I still think it could use some lead guitar, and not just breakdowns and heavy blast beat riffs. Then again, it would seem like it would just turn into death metal.
My main problem with metalcore and post-hardcore is its strong similarity to pop music. To me, metal is about being different from other genres, and then you see bands come out with mainstream clothing breakdowning, power chording, and screaming away in the name of metal. It just is not metal to me.
Oh, and don't get me started about nu-metal...