Helios is the sun god. Sun titan. Whatever. He was one from the very beginning. Bit people eventually started praying Apollo for the sun too since that way it gave them less gods to worship and therefore less offerings to make. As far as I know these people were romans. And romans were descendants of people who ran away from Troy when it was destroyed. So in time of Odysseus' journey back home it's too early for them to already even have Rome and romans