Lots of crazy and illogical theories around Admirals = Yonkos but I feel as though Oda couldn’t have made the power gap more obvious.
1- Garp said the World Government couldn’t even take on 2 legends at the same time whilst referring to Rayleigh who hasn’t even got close to the manpower of a Yonko.
2- Sengoku states they can’t overcome Whitebeard with military might. They openly admitted they needed military tactics and sneak attacks to defeat him.
3- They had to have Whitebeard’s son stab him through the chest and Whitebeard have a literal heart attack on the battlefield all the while saying ‘he’s old and nothing compared to what he was’ before they were able to seriously injure him (not kill him).
4- Admirals are only portrayed to be as strong or slightly stronger than the top tier commanders of a Yonko crew. For example Marco was fighting on par with Kizaru and actually overpowered him until he had sea stone handcuffs put on him. Jozu was fighting evenly with Aokiji until Whitebeard was dying then took a sneak attack. Sabo was fighting completely evenly with Fujitora.
5- Even Doflamingo had no problems straight up attacking Fujitora and stated that he might try to kill him. Can you imagine him doing this with Kaido? No, he was so afraid at the thought of Kaido coming for him.
6- When Whitebeard sent his first attack towards the stand all 3 Admirals had to stand up with their Haki to block it, do you think if 3 Big Moms were there they would all stand up to block it?
7- It took Akainu several hits on what was basically a sitting duck Whitebeard who was having a heart attack to bring him within death range, whereas it only took Whitebeard 2 attacks to take Akainu completely out of the fight for 10 minutes.
8- Whitebeard slapped Ace through a wall when he was sleeping, whereas Aokiji couldn’t even slow him down and the only reason Akainu killed him is because he came back to save Luffy.
The World Government hates the Yonko and wants them dead, if they had enough military power to stand an assault from 4 Yonkos they would simply defeat them one after the other without a problem since they aren’t allied and they aren’t hiding.