The issue is WB is not in his 20s he's in his 30s here. I can't just chalk it up to youth.
WB ain't Oden to me. Ray was introduced as a right hand man. This is different.
My point simply is that Whitebeard was always that guy.
Ultimately, Whitebeard wasn't even interested in traditional piracy. He wanted a yakuza like family based on loyalty, honour and care for each other; where he would be the head.
It just turned out that the pirate crew he built after Rocks became what he wished for.
Whitebeard just wanted that kind of "family". He stayed with Rocks, because he found that there - a place to hang out and drink with people he liked.
He would've been the leader for that family in a normal scenario, but it takes extraordinary type of captain to make someone like WB follow him. Rocks was simply
that guy.
Just look at the comparisons with Zoro.
Zoro isn't interested in being a pirate or mafia. But he isn't against being a member either, on the condition that HE is the boss. It's the reason why he turned down Baroque Works. The only condition to join is him being the leader. Zoro being confused as the captain was a common theme until Dresrossa even (after which SHs became simply too famous for this theme to be played out again).
It takes an extraordinary type of captain to make someone like Zoro follow him. If SH crew suddenly disbanded due to Luffy's death, Zoro would be the next big pirate captain of the new gen.
These themes are put in place to demonstrate the captain simply being that damn impressive.