There is plenty of reasons for Marco be the chosen One for 1 division
Name 2.
Experience? Nah, Marco was a rookie.
Loyalty? Maybe, but along with experience, there are others who had been there for longer and qualify more.
Seniority? Nope, again Marco was a relative noobie.
Leadership ability? Maybe but again unlikely for a rookie. He was just being bossed around by whitey bay last chapter after all.
Strength? That’s highly plausible, Marco did in fact have his mythical Zoan fruit for at least 2 years now.
Besides, all of the reasons that might theoretically qualify Marco for YC1 aside from strength, directly disqualify Oden to hold any YC rank at all as their is a negative correlation between what qualifies Oden and what qualifies marco.
The only plausible explanation for this, the only one, is that Marco is stronger than Oden. Just like the only possible explanation for Oden getting the YC2 rank is his strength.