Yet Luffy, the same example you used, in 16 years old was weak as shit compared to the level of power you think Marco had.
I don't know why Whitebeard gave Oden YC2, i said my theory i already, either there was a YC1 that died before that and we don't know him, or there wasn't a captain to the 1st division because Whitebeard was still active, he only put Marco in charge of 1st Division after Marco got older and stronger, and when Whitebeard started getting older. That's my reason for it. It makes much more sense to me than Marco being YC1 by 16 years old, and not having improved at all in the last 30 years, wtf.