Derivative

I'm not sure what's so bad about "derivative" fantasy worlds. I guess what I write is "derivative". See, I was really excited a few days ago, I saw an editor who sounded like someone I would love to work with, but then I read that he did not fantasy worlds that were "derivative in any way".
I like derivative. I mean, I read original fantasy worlds, but sometimes it's cool to see a fireball, and elf, a dwarf, a dragon and all that jazz. Dwarfs hate elfs, magicians aren't great in combat, trolls burn, ogres are super tough but not all that smart.
I guess these are tropes of fantasy as originated by Tolkien and then perpetuated by D&D, but I enjoy them.
I am reading a D&D graphic novel and it is everything D&D was when I was a kid (IDW Publishing rocks by the way). In addition, I am playing a game called "Legend of Grimrock" and it makes me feel the same thrill I used to feel around a gaming table.
I like reading Warhammer fantasy books and I enjoy some D&D novels. I used to love Salvatore, but it got a bit repetitive, but I still recommend him to people who have never read his stuff.
So, what's so bad about derivative? Can't you tell a good story and be derivative?
When I think derivative, I think Westerns. They have all sorts of common elements, but people love them. Couldn't we do the same thing with fantasy?
I don't know, but I think I will continue being a bit derivative while applying my own touches. It works for me. I guess that's my art. We'll see where it goes.