Leigh Brackett and Margaret St. Clair are both women.2. I think they have also influenced D&D in a negative way because not one of those books is by a woman and/or person of color (as far as I know - and even so, one or two is surely insufficient), and you can't say imaginative books that meet those criteria did not exist in the 1970s. . . it is just that Gygax and others didn't make the effort to look beyond that narrow view of influential authors.
But yes, Gygax could and should have read more widely. The lack of LeGuin and McAffery in the 1970s is striking. White Dragon wasn't out as Gygax was writing the DMG, but her dragon stories had been around for years and well-regarded. And LeGuin was already long since a legend.