They were up against the WORLD government, the Marines and Sichibukai balance out the 4 Yonko, no 1 Yonko with his/her crew should be able to fight the WG if the Marine+Sichibukai side would be completely serious and had gathered ALL their forces they would imo annihilate even the WB pirates and Red Hair pirates together
WG: Garp, Sengoku, Akainu, Aokiji, Kizaru, Mihawk, Doflamingo, Kong, The Gorosei, Kuma, whatever the hell Vegapunk is capable of, the VAs, CP-0, ...
vs
Pirates: Shanks, Whitebeard, Backman, Marco, Yasopp, Lucky Roo, Jozu, ...
I give this to the WG quite easily, imo it would take all 4 Yonkos and their crews to be able to say it's an equal fight and it would depend on their second in command to determine who would win
I do think that Yonko level in itself is a bit above Admiral but the gap is very small, not to mention that Yonkos and Admirals can cross into each others tiers because not all Admirals and not all Yonkos are equal