Appendix N to the Dungeon Master’s Guide is an ever full well. Each dip of the bucket brings up something thirst quenching. Gary Gygax’s pulp influences were as broad as they were deep. Some feel that D&D is best seen as an immersive plumbing of pulp Sword and Sorcery. There is probably much to support that opinion. But even a cursory reading of Appendix N indicates that he did not limit himself to the sub-genre. He mined science fiction, historical fiction, and epic fantasy.
Does the Sword-and-Planet (also known as Planetary Romance) genre qualify as Sword-and-Sorcery? Or, more precisely, can it?
Yes. Next question.
Wait, you want some sort of explanation rather than a blanket agreement or denial. Fine.