@desa:
Logic should tell them that the admirals should all be kept busy
Yes, but it's a war zone. You can't tell what's going on across the plaza; you're lucky if you can tell who is fighting 100 feet away. Plus, you have to worry about what's going on near you, so you're distracted. And everyone was simply retreating until they saw Akainu barreling down on Luffy. For all they knew, Aokiji and Kizaru were dealing with the Blackbeard pirates at that point. Even CoO isn't perfect, and a chaotic war zone like that is probably just about the worst time to be trying to locate specific people with haki.
And the commanders clearly seemed to be loosing with Curiel burning in the ground.
Curiel definitely seems to have gotten beaten, yes, but that's not really very telling. Again, they knew Akainu had backup coming in, and they were only trying to enable everyone to retreat.
And if a massive attack could take care of akainu for the rest of the war they probably would have since they have to hurry and they guy killed Ace, bring Whitebeard to the death door and is trying to kill them all.
But even a massed attack might not be sufficient to kill Akainu, and it might give the opportunity for other marines to flank them. In fact, as we saw, they got flanked despite that, at least by Aokiji. Nevertheless, the strategy they used was better for the goal of helping everyone escape, even if it meant not getting vengeance against Akainu… and Whitebeard's final order to them was to escape.
WellAkainu appeared at the war just like them.
This is true, but he was also one of the main antagonists of the war; his role in the story of the Marineford War offered a better chance to show off his destructive powers than what the commanders got, and logia powers are generally flashier/more visually impressive than a lot of what we see otherwise; unless you can directly compare the effects against someone/thing who has no unusual resistance/weakness to either type of attack, you can't really gauge effectiveness of two attacks. Mr 5's explosions looked pretty impressive, but he was a total weakling, while a single unnamed slash from Zoro was able to cut through the massive stone doors at Enies Lobby.
Well Jozu got fucked in one move. A surprised one. But Jozu did the same to start the fight and Whitebeard doing the same to Akainu is considered legit.
I consider there to be a substantial difference between the circumstances, and therefore, the implications of the outcome. When Jozu attacked Aokiji, Aokiji was caught off guard, but because he was fighting someone else at the time; he was prepared to get hit, he just wasn't expecting a hit from Jozu. When Akainu was hit by Whitebeard, he was warned by his men first, and by any reasonable set of expectations, was ready to get hit at any time.
Jozu lost specifically because he was distracted from the fight by what happened to Marco. He should still have his head in the fight for pragmatic reasons, but the way it was portrayed clearly suggested he lost focus and was distracted from fighting completely (which is also how the VAs got kairoseki cuffs on Marco moments earlier). That's very clearly why the events were portrayed the way they were; Marco and Jozu were shown briefly able to fight the admirals on equal terms, and were defeated due to both getting distracted from their fights. Maybe they're weaker than admirals, but the whole reason Oda went to the trouble of panels and dialogue of them getting distracted was to leave it ambiguous about whether they are actually weaker or not.
And Vista is weaker than Mihawk who is a shichibukai.
First, Mihawk isn't just a shichibukai; he's the strongest swordsman in the world. That title implies something about just how strong he is. Every marine is trained how to use a sword, from what we can tell, and many of them - including vice-admirals - seem to fight primarily using swords. We've even seen that the marines have outright swordsmen like captain T-bone. Yet a pirate is the world's strongest swordsman.
Secondly, Vista is a renowned swordsman - probably one of the top handful in the world, as the top swordsman of the Whitebeard crew, and one recognized by Mihawk - but that doesn't automatically make him the strongest among the Whitebeard commanders.
Knowing that Vista is weaker than Mihawk tells us essentially nothing about comparing the admirals to the top Whitebeard commanders.