Honestly, Coby is one of the worst characters in this series.
Nothing interesting about him. Watching paint dry is more interesting than Coby, plain design, plain abilities, dude's jaw is hitting the floor everytime we see him because he is out of his element/league in every situation.
The only thing we know is Oda will shoe him in as an Admiral one day. That's his entire character right there.
Luffy fangirl who is guaranteed an Admiral position. That one sentence is Coby the character.
Ignoring all of that, objectively, Coby is obviously not going to be a top tier by the end of this series. Not unless Oda wants this manga to go down as the shittiest of all time, make Bleach look like a masterpiece.