Ace was a Captain/leader of the Spade Pirates before Whitebeard came to him. Its different with Yamato.
Even in the flashback, he is the strongest among Sabo and Luffy. So, if Oda decided to give Yamato a CoC. Its a inconsistency again.
Even in the flashback, he is the strongest among Sabo and Luffy. So, if Oda decided to give Yamato a CoC. Its a inconsistency again.

Confirmation Bias.
