So this boils down to we define god differently. To me he's from the universe(not another plane/dimension) and mortal so not a god.
That describes most of the actual gods of the Marvel universe, though. Whether Asgardians or characters like Hercules, who are explicitly gods in the comics (even if the movies shit on the idea of Asgardians being gods as opposed to aliens). Ironically, the actual transcendent beings who exist entirely beyond the physical (like Death and Eternity) usually AREN'T referred to as gods by anyone. They're basically "beyond" godhood.
Thanos is actually an Eternal. And Earth's Eternals have repeatedly been referred to as gods or mistaken for them (the most common being Zuras, Thena, and Makkari - who are usually conflated with Zeus, Athena, and Hermes/Mercury, respectively). They even live on Mount Olympus. Even the ones who aren't usually considered gods still inspire tons of mortal legends (like Sersi, Gilgamesh, and Ikaris).
Thanos' brother is Eros (aka, the Greek God of Desire). And Thanos himself is specifically named to evoke Thanatos, the Greek God of Death.
Once again we just have differing opinions. People thought Egyptian Pharos where God's. Doesn't make it so. My step father is a huge marvel geek and even he says thanks isn't a god. Dude owns like 1000+ marvel comics so I tend to take his word ---
Cid- "looks like that overgrown lobster just got served!" Bartz-"with cheese biscuts AND mashed potatoes!"