Notice how Sanji is canonically confirmed to be the closest to Joyboy as a character.
Sanji is called a "Spear"
Joyboy has a Spear.
Sanji is holding a spear in a Viking centric colored page.
Then according to Norse mythology about Odin's spear:
Gungnir (Odin's Spear) was a symbol of power, protection, and authority. Its name means "the swaying one" in that it brings people to Odin (Simek, 124). Gungnir, like Mjolnir, was made by the dwarves and was used by Odin to sacrifice himself to himself.
This is supported by Mihawk and Greenbull's statements like you said.
Narrative wise, Sanji has a crazy potential. We only know about Sanji's full backstory so far, we have yet to discover what his Diable Jambe's origin is so expect some crazy lore for Sanji in the future. And it's not even EOS yet. Sanji really are one of the most intriguing characters so far due to his immense plot involvement and development. Good stuff.