Let me ask, how strong do you think CURRENT Coby is… Because what you want for Coby versus how much time is left in the story for characters to get stronger HEAVILY hinges on your idea of how strong he currently is
He should currently be as strong as a Yc3 honestly. I place him at the very same level that sanji was before sanjis new lineage gene's powerup. As hard as that may seem to believe oda is doing several things that suggest he is indeed strong
1. He hyped up the potential capture of boa Hancock. And he futher went out of his way to not show any other combatant on the same ships as coby heading towards her.
2. He has been hyping up Coby's growth rate from jumping to a scrub that can't fight to using cipher techniques in 6months. And now in 2 years he is promoted to marine HQ captain with his post being in the new world under akainu. Akainu love him or hate him he respects the power of competent soldiers in battle.
3. On top of this this dude is now apart of a secret organization in the marine faction that is a polar opposite of cipher pole within that same 2years?????
4. He also allowed coby to take part in guiding and protecting a royal nation to maregious with kyro stating that the dude (coby) is strong and modest.