Well yea, Aokiji would be a good leader. He's well-liked so they'll listen to him and while lazy, he isn't stupid either. While he is lazy, Marineford showed that when Aokiji needs to get the job done, he gets it done.
Doflamingo was also laughing while Whitebeard was tearing Marineford apart and yelling out how much fun it was. He was eager to go to war with Whitebeard, so he's laughed at Yonkos too. And you're talking like all the Admirals are always gonna be in line with each other. Laughing at Fujitora but being wary of Kaido simply means that Kaido is more ruthless or has a better chance of killing Doffy than Fujitora does, not that Yonko>Admiral all of the time. Did you ever stop to consider that Doffy was able to laugh at Fujitora because he knew that Fujitora can't do anything to him due to his status as a Shichibukai, which Fuji has no grounds to remove, while there's nothing stopping Kaido from killing Doffy if he wants due to his ruthlessness? No, I'm sure you didn't, you were connecting the wrong dots instead.