I go off the simple fact whitebeard was and always has been portrayed stronger, he was taking on literally everybody, if it was fresh from the get go I don't see akainu surviving. He only survived what he did because he has more durability when it comes to haki then anyone else in the series(thats been shown so far)
Whitebeard was in way worser shape regardless of a sneak attack when starting that fight, if akainu did not evacuate I don't think he would have survived especially if white beard had not had any previous encounters.
In the fight with akainu and the other admiral, where one half was ice and the other lava, wb would've just sunk both halfs even while sick