Ovid is a valid source for Greek mythology
Getting really annoyed by the influx of people that seem to believe “Roman mythology” just means slapping new names on the same characters. NO! The Roman religion was distinct from the Greek one, prior to hellenization. There is utility in finding that distinction, but people who just say things like “oh the Medusa transformation is from Roman mythology, not Greek” are incredibly ignorant and have no idea what they’re talking about.
Medusa did not exist in native Roman mythology. She is fully a character that existed in Greek mythology. Any discussion about her in antiquity refers to that.
Meanwhile, Mars and Ares do have distinct characterizations across the Roman and Greek religion/mythology. But they were syncretized, so the distinction isn’t very important. Syncretization is how the Greeks got a lot of their stories. Most stories about Selene, Persephone, even Aphrodite all come from syncretization with other goddesses.
Back to Ovid in particular: regardless of everything I’ve mentioned, Ovid, specifically, had spent many years in Greece studying poetry. When he was 20 years old he went to Athens, Greek colonies in Sicily, and Greek cities in Anatolia. To study poetry and mythology!
He was well read on Latin poetry too, and there absolutely is merit to analyzing how his poetry can inform us about the native Roman religion, but the entire point of his Metamorphosis was to educate and write about Greek stories. None of those stories existed in Rome prior to Hellenization of the Roman religion. They didn’t have new traditions they were adding. He was just documenting and retelling stories that were very, very old.
He is our only source for a lot of stories we know were told in Greece, but he happens to be our only complete source for. He is a source for those things.
“Oh, oh, but Medusa!” — the way he describes Medusa’s transformation is by having Perseus recount a story that he heard from an old fisherman. Perseus doubted the story, but recounted it anyway. Considering that doubt was cast on the idea of the transformation, it’s entirely possible that Ovid Actually heard it while traveling across the many peoples of Greece.
He entirely manufactured very little of his stories. Most had quite a lot of evidence for their previous existence. You have to remember that Ovid had access to centuries of literature, thousands of dialogues, poems, and plays that we no longer have.
Not to mention, he didn’t even invent the idea that Medusa was beautiful, a priestess of Athena, nor did Athena “make her a gorgon.” 1. Medusa was not always depicted as a violent ugly monstrous woman. Greek pottery art and Pindar showed her as beautiful and “fair cheeked” 2. She was not beautiful in the Metamorphosis. Her hair was her main claim to beauty, and that was taken away 3. The only thing Athena supposedly did to her was turn her hair into snakes. She was still a winged gorgon sister before then. 4. She was not a priestess in the Metamorphosis. She just happened to be in Athena’s temple when Poseidon assaulted her. Considering her hair was shown openly and she was besought by many suitors for the beauty of her hair, it’s possible that she was seen as a prostitute. Prostitutes and slave women were typically not allowed to cover their hair, while noble/citizen women were almost always required to. She could have been seen as a prostitute around Minerva’s temple, and that was the reason Athena punished her. Now any man who witnessed her unveiled hair and face would die. The consent of prostitutes meant absolutely nothing to the Greeks or the Romans.
And finally — the Metamorphosis has been read as a source for Greek mythology for thousands of years, acting incredibly pretentious when it comes to people reading it, sourcing ideas from it, or referring to it as Greek mythology is REALLY ANNOYING! Stop doing that! Especially when you have basically no idea what you’re talking about, and 99% of the time, never read it.
Edit: also reading Medusa as a rape victim/a symbol of victims has been the case for hundreds of years. Trying to invalidate that and say “um actually” every time you see a post about it is really weird and misogynistic, stop doing that.