I think it’s very likely that the guy Silver Axe is fighting here is in fact Marco’s dad.
My primary reason for thinking this is simply this. Oda has shown repeatedly shown the meeting of the captain and his right hand man, and the formation of major pirate crews.
We saw Roger and Rayleigh’s meeting
Big Mom and Streusen
Kaido and King
We haven’t really seen this for the WBP. We saw WB and Oden, but WB had already formed his crew by then.
Given how God Valley is basically the start of WB’s solo career as a pirate, I’m guessing Oda will touch on the start of the WBP in this flashback. Hence Silver Axe vs the Marco clone. That probably is his dad, a member of the holy knights.
My guess is WB saved Marco in GV, ultimately leading to the two forming the WBP afterward.
