We know what Oda is going for, but he's been pretty lousy with showing Koby's evolution.
When he and Luffy met, Koby was a nobody.
In W7, he was a few steps behind Luffy combatwise, but already on his way to gaining power.
We've seen what he's done with Garp and SWORD. Next time him and Luffy meet, Koby might just prove to be a challenge.