The Marines needed all 7 Warlords. They needed it on their turf where they had the highground and could lock WB in while taking away his footing and being able to destroy his ship. They also needed someone on his side to weaken him. And they also needed one of his commanders locked up to provide a constant distraction.
And on top of all that, they needed WB to be dying already, and to suffer minor heart attacks during the battle, which of course caused his commanders, people who viewed him as a father, to abandon their fights, where they were holding off the admirals, and try to help him, thereby leaving their backs exposed for the admirals.
And on top of all that, they needed Blackbeard to come and deliver the killing blow with his entire crew.
Is that overwhelming power? There is a reason the Marines aren't going around trying to take out the Yonko one at a time.
I think an accurate comparison would be between the US and Russia. Both are nuclear powers, and both have very large militaries. However just looking at their expenses on defense and the global positioning of its militaries tells you that the US is absurdely more powerful. However, to defend itself from Russia, the US needs Europe and created NATO for that reason. Also, despite local conflicts and open hostilities between the two, an open war never breaks out.
The thing is, when it comes to war, once you are past a certain level of military progress, there will always be unavoidable collateral damage, no matter how overwhelmingly powerful you are.
You can't take one Yonko at a time. When they picked a fight with Whitebeard, Kaido and Shanks were already on their way. A single conflict already involved 3/4 of the Yonko.
Also just to point out, none of Whitebeard's commanders have shown any capability whatsoever to damage an admiral. Jozu and Vista would loose 100% of the time, and rather sooner than later. Marco can only hold his own due to his fruit, but the Admirals can fight for weeks, so it doesn't matter.
They also didn't need Blackbeard at all. Half of Whitebeards head was already gone at that moment and Whitebeard knew he would die even beforehands, hence why he chose to sacrifice himself. It was only a matter of minutes for him to bleed out from Akainu's attack. Had Blackbeard not appeared, Kizaru or Aokiji would have finished him before he could sink the island.
The moment Whitebeard went to close quarter combat with an Admiral, he took lethal damage, whereas the Admiral got back up after minutes and continued to steamroll his way through. Even at the start of the battle, the Admiral's showed no difficulty facing Whitebeard, as Aokiji just shrugged of Whitebeards Haki imbued attack. I think there is also a panel of Akainu blocking Whitebeard's Bisento with just his feet, his hands in his pocket.
The reason why the Yonko always get evaluated as more powerful han the Admirals is simply due to appearance, to be honest.
80 year old drunk Hulk Hogan who dies standing
Crazy drunk Mongol Warlord who transforms into a dragon
A fat lady who sings, then takes your life
The most piratey pirate, all consuming darkness
A cripple who is equal to all of the above
vs
Japanese Actors in suits.
There is no single indicative in the Manga that actually confirms Yonko > Admiral. Quite the opposite, actually.
But would they really ally with each other? Big Mom and Kaidou were part of the same crew but became enemies until Luffy.
And the Marines would never take action unless they know they have overwhelming power, so the Emperors would likely not need another Emperor to fight the Marines.
I'm assuming she could be the equivalent of Katakuri if not stronger, just because of her beauty and devil fruit alone. Otherwise she's shown to be an incredibly competent fighter with how she's damaged the Pacifista, but I'm not sure how she'd fare in an actual fight.
The thing is, defeating a Pacifsta puts you on a level with Pavlik. Who? Yes, that basically answers how much this is worth by the standards of New World captains. Basically, it appears once you are a Haki user, you can bypass the armor of the Pacifista, turning them into a non-issue.
I actually agree with you and think Hancock is crazy strong but her feats don't give that away. She is, as of now, definitely the most overrated character in One Piece.
If we go by actual feats of female characters, the list would probably be:
1. Big Mom
2. Nami
3. Smoothie
The number two and three spots should tell you something isn't right here and that's true. The thing is just that the female characters have comparably less feats and this is mostly for ethical reasons. Oda wont draw gory fights involving (beautiful) female characters, however that greatly limits the design space for such fights, leading to many female characters comparably lacking feats. That's why Nami places second, because a fed up Zeus Tempo is the most powerful attack displayed by a female character, and something aside from her, only the #1 can do as well. Smoothie's giant slashes never hit anything, but at least they were huge.
And we can't even evaluate much more than attack power. Because the females never get critically injured, we can't really evaluate stamina, and we can hardly evaluate speed either.
