Theory: Kuzan will serve as Koby's "Kaido," during the Final Saga.
Hello again, One Piece power scalers, it's Esmund.
Let me preface what I mean by "Kaido":
Simply put, it's the idea that a character fights a top-tier and earns multiple buffs during the said fight to—in some way or another—defeat said top-tier. Similar to Luffy's fight against Kaido.
Luffy evolved multiple times before and during Roof Piece and his 1v1 matches against Kaido and carried himself as a Yonko-level combatant.
Similarly, I'm convinced that Koby will likely fight Kuzan and, by defeating him, will earn himself as an Admiral-level (or Yonko-level) combatant.
Narratively, this may be pretty convenient. Rather than mimicking the Roger + Garp vs. Rocks situation with their parallels: Luffy + Koby vs. Black Beard, we can have Luffy defeat Black Beard on his own, while Koby takes on Black Beard's strongest crew member: Kuzan.
But I may be pushing it.
I wouldn't know what kind of buffs Koby will be getting, but leading up to it, I reckon it'll be related to awakening CoC and ACoC, most likely.
Thank you for reading; have a wonderful day.