You guys need to understand one thing about Akainu
He ain't just a obstacle villain who Luffy needs to beat to reach his goal, he's the guy cause the most traumatizing moment of Luffy's life. In any piece of media, when a loved one is killed in front of the MC, he always gets he's revenge in some way.
That's why need to be a LEGIT moron to truly believe Akainu is Sabo's opponent. It's so dumb to think a guy who got reintroduced in later Dressrosa is a good choice for fighting Akainu.
Luffy vs Akainu ain't just a fight, it's personal