*Fun Fact:* Oda originally planned for Whitebeard to kill Akainu here but his assistant/editor suggested keeping him alive for a more interesting story.
Akainu is strong, but he got mopped with Whitebeard. Whitebeard already had hundreds of wounds, is old as hell, and has stage 5 cancer, and still beat the everloving crap out of Sakazuki
If Whitebeard didn't had his injuries, Akainu would have been dead. If Whitebeard was younger and in his prime, Akainu would have been dead instantly. Still having Akainu being defeated by an injured old Whitebeard is very insulting and hurting his pride.
They're not biological brothers - but they're oath brothers. They see each other as brothers. And you can't deny there is a similarity between Ace and Luffy - not quite them looking like each other but there's something similar about their appearances.... You can believe it even when you can see Roger's face in Ace (he looked a lot like his father when his hands were bound and they made him kneel) and Garp's face in Luffy (though Luffy's face is rounder, younger and happier rather than older and meaner like Garps, they have a really similar smile).
And people say Admiral are stronger than a yonko one yonko old can't use haki anymore mortaly injure the whole fight just destroy the best Admiral of the Navy
A Prime WB would have finished Akainu in 2 powerful Advanced Haoushoku Haki with Guru Gura no mi imbued attacks, since one was enough to defeat a Prime Oden This guy was a nightmare
The reason why there were impact frames on the part where Akainu shaves off part of Whitebeards mustache is because Whitebeard actually lost almost half of his entire face to that attack in the manga. It was just censored to his mustache for the anime.
