Technically you are right, before these spoilers I also thought the same but Coby's growth is really insane. In last chapter, he was completely helpless and now he destroyed Pizzaro's arm at the next chapter? By mimiking Garp's technique? How is that even logically possible?
Now that Coby has both CoA and CoO, it isn't farfetched to think he'll exponentially grow, knowing Oda. Will he face Kuzan yet? Definitely not. But somewhere near EoS or even EoS? It's possible.