Assume that the second strongest in Whitebeards crew is Marco. He is strong alright but in my opinion he is not strong enough to represent a first mate, or is he?. Lets pretend that Cracker is the second strongest in Big Moms crew. He seems to be stronger than Marco, but, anyway, you can change the discussion, so, is Marco stronger (or equal) than Cracker and would his strength be fitting for Whitebeards first mate/son. xD had to add this "son"