Or the type that is most commercially successful in current tastes & trends. it is after all a business and the writer, no matter how hard they strive to make their voice unique, is trying to make a living. I've followed Charlie Stross's writing about the business side of the industry and it's very common to work with editors & agents to ensure they're writing in a marketable sub genre. For example, imagine a writer that had a story outline set in a alternate timeline epic fiction where magic existed, but current tastes among readers looking for epic length books skewed towards space opera. An author might without too much difficulty map many plot points onto space opera settings. Magic becomes advanced technology. Empires can exist in both; historical details can be mapped onto the fictional societies & their history, etc. At the same time, the tropes specific and unique to alternate timeline historical fiction might be adapted and morphed in the space opera genre to create something a bit more unique.
But a writer could not easily make those kinds of adaptions without being well read in the umbrella genre.
I think people underestimate how much reading will help you write. You can't spend your life reading and not absorb some information about structure, style, and the language. As a kid, I went to the lower levels of spelling bee competitions pretty much every year because the kind of words they throw at you at lower levels are largely words I would encounter reading Jules Verne and the like. I'd eventually get knocked out because I never studied the official list of spelling bee words, but my voracious reading held me in good stead for most of it.