The government gathered all their strength (including the 3 admirals and the 7 Shichibukai) to fight only one Yonko and his allies, so how can they defeat the 4 of them together??
That was a small fraction of the Marines. Lets not forget they didn't have
CP1,CP2,CP3,CP4,CP5,CP6,CP7,CP8,CP9 and CP0-Aegis there...
On top of that, neither Kong nor the Gorosei fought.
Plus, the Admirals and the Yonkou are on the same level. Considering there were 4 Admirals present, and the fact they did in actual fact completely annihilate the WB Pirates and allies, it would be a walkover against any Yonko now, with:
Kong, Sengoku, Garp, Sakazuki, Borsalino, Issho, Ryokugyu, 5 Gorosei, Mihawk, Kuma, Hancock, mystery Shichibukai and CP0 as well as all the Vice Admirals and any other very strong combatants we don't yet know about