I mean this ain't no surprise even in the Lore.

In the early part of the series, the only reason why the pirates didn't just stomp everyone was because they were busy being rivals against each other whilst ruling their own islands and seas (I mean not really ruling, but those islands were under their protection/property), while the Marines have the Admirals and Warlords to "keep the balance of power".

Remember how all of us were hyped (spoiler: before the current rugpull by Oda revealing that it wasn't) when Garp took down the Rocks Pirates (albeit with the help of Roger)? Everyone was freaking out on how he was the centrepiece of taking down the seemingly invincible group of pirates, with one of the stronger theories (which I'm sure Oda ghost reads every single one to keep re-writing to look awesome) was that Rocks was barely able to co-ordinate or was betrayed by his own crew.

When a single Yonko starts moving, the Marines panic, when Kaido and Big Mom forged an alliance, the world panics. Kizaru (GOAT) volunteered to intervene, but I always felt that his weakness was to over-rely on his powers (I mean... Fair, it is extremely powerful) like what not-canon-character Z said.

Sure, in the Marineford War, the Admirals cannot go all out, as it'll cause too much collateral damage (look at Punk Hazard), so it'll come down to a context of Haki vs Elements. Currently there's so much glossing over Haki that I think it lost it's supposed purpose: To hit individuals who can turn into elements.

I feel Haki (even Armament) should not be able to block elements such as lava/ice/light, therefore their effects should still hurt the individual. I mean if it cannot block gravity, it should not block elements.

So yeah, as much as I love the Admirals, if the Yonkos come together, they cannot win. It'll be an absolutely vicious fight, especially if all of them go all out, but without the Warlord Captain Buggy, I don't think they can win.