Ah. I see. "Those people" need to zip it; the ancient Greeks were already saying, "There is nothing new under the sun." Every single theme has been done already in some way, shape or form. Creativity lies in what you DO with the themes - combine them, tweak them, take them in a non-standard direction, etc.
Just keep reminding yourself that Lord Kelvin... yes, the guy for whom the temperature scale was named... tried to close the patent office in 1900 because nothing useful was left to be invented.
Don't stop trying to do something new, because everything had to start somewhere. If nothing else, as Grandmaster Robert Heinlein once pointed out in "Spinoff", a researcher will inevitably find
something of interest, even if it has nothing to do with the original hypothesis.
There's nothing wrong with combining "supernatural conspiracy" with "Wild West", because all the stories you write remain uniquely yours. Whether literature professors sniff out (or project) links to anything in literature prior to that is their business; your business is in writing the best stories you can, selling them for the best return possible and making enough money to live off.
Good luck!