You need any type of built up to justify a future fight. Koby won't go from no comment to I'm gonna kill Aokiji. In an entire arc Oda surely could've squeezed in one tiny battle that builds up something, instead, when Koby recovered he said he has to stop Luffy's dream.
All we know is Koby is going after Luffy next
All we know is Koby is going after Luffy next
All I care about is kuzan staying rogue and going down as BBP.
I would definitely prefer Smoker over that cry baby koby but with complete absence of smoker I really don't have anything to put a case for him