CoA also has shocks, like for example Luffy vs Ulti but talking about Koby, Koby doesn't have CoC, much less AdCoC not only that but also Koby doesn't need CoC, he does need a power development to be able to rival Luffy but there are other ways to do this. ACoA, AdCoO with the accompaniment of Rokushiki techniques. Also, you said you saw it in a filler so what's the credibility??
Toei always spoil us, with something, openings, Movies or Fillers Even if isn't a canon source.
Helmeppo hyped Coby Haki(Observation one), Coby know it in early Days of Mariens.
Was trained by the biggest Marine Haki user in OP world.
Him having Rokushiki is okay since any Vice Admiral has.
Master Rokushiki,AdvCoA and AdvCoO and his physicall strenght will be top tier.
That's why i am speculated that Coby already used a AdvCoA in a Filler, because was something much close to AdvCoA than a normal Punch.