You do know Oda was just talking about Ryuma, not Zoro, right?
I'm only going to bother saying this once. But Oda's main template like DB is JTTW (Journey to the West.)
In JTTW you have Wukong as MC, but Sanzang as deuteragonist, and the actual ending and journey being about Sanzang.
Also known as Tripitaka (Three Baskets).
In One Piece, Luffy is Wukong, or at least half of him. Personality, Monkey ref, the headband (his Nika brows), all around imagery and powers. Nami is the other half, she's got the cloud and staff.
SANzang is self explanatory. The monk that travels with Wukong to collect the scriptures. Sanzang is the one that reigns in Wukong's unruly behavior, keeps him on the path of right, and is the one of the whole group that shows mercy, kindness, and compassion. Sanzang is split up between Sanji (Compassion, kindness, mercy, "SAN," and keeping Wukong/Luffy reigned in.) | Robin: Collecting the 'scriptures' or in this case poneglyphs.
Also, in every Omake Oda makes, Sanji is always named SANrandomnameattached.
Thus Sanji and Robin fit more to deuteragonist as the representation of Sanzang.