He was at his full strength and rage when he attacked Akainu and while he destroyed MF's foundations he couldn't do anything to Akainu himself. Aokiji is just as insane considering he managed to fight Akainu for 10 days straight! And then we have Kizaru the madman, who showed absolutely no fear in wanting to go confront two Yonkou.
WB wasn't at full strength, he acknowledged that in the war. Even if we judge the Akainu vs WB fight by boxing standards Akainu got KO'd at the end. Ref would count him out. I give him points for burning his face and his stomach. Still I'd expect Aokiji to pierce him if Jozu hadn't interfered. Same as how the many fodder marines pierced him with blades and the BB pirates bullets pierced him. It's just that magma is that much effective.
However Akainu got KO'ed and if WB was to actually finish the job Akainu would have died .He was at WB's feet, at his mercy and could only curse him as WB let him fall. The fight didn't go the distance. It wasn't a 3day fight like the Rodger vs WB fight, or Ace vs Jinbei 5 day fight, or the Akainu vs Aokiji 10 day fight. He was beaten in very shot time. There was no parity. He was being knocked down a lot in the fight and didn't force WB to give ground at anytime. That is what the strongest admiral could give . He was effective though, there is no taking that away from him because long term WB was still going to die.
True WB blindsided him at the start but Akainu should have been more aware. Either his observation isn't great or he is too confident in his strength. We have WB beating Ace in his sleep and Big Mom almost killing some straw hats as she slept. Akainu has no excuse letting his guard down in a war. He is in his prime and if he was equal he should do as his equals do. He has the aggression, drive and will though and that is what can trip you up because we see Luffy do the same time and again. Good traits in a fighter. You say he got up but after how long? If you get Ko'ed doesn't mean you won't regain strength. If it was a more ruthless individual Akainu would have been executed there. As Akainu was out WB went on to beat BB in a fight in a more weakened state.
When the Yonko have clashed , the haki effect is different. Akainu and Shanks clashed we didn't get that. Admirals get stalled by YCs in prolonged fights. I don't see the YCs doing that to actual Yonko. Oden got swept away by Rodger, Queen got manhandled, Luffy got Ko'ed by a drunk Yonko.
TL:dr: Admirals are a huge power and can take the fight to a Yonko. I'd still bet on the Yonko winning 3 out of 5 times though at some personal cost in a fair fight.