The balance works as long as the yonko are not allied.
This.
Which is the reason they don't want Yonko to be allies and they send their forces to stop Shanks from meeting WB because they afraid they would join forces.
I still don't know how people can actually believe Marine forces + Shichibukai can counter/match 4 Yonko if they fight at the same time.
People who believe this must be consist of incredibly biased mihawk supporters and akainu supporters. Otherwise its impossible to believe that.
Non-Yonko BB fought FA Sengoku + Garp with no problem.
Yonko underlings like Marco, Jozu and Beckman equally fought or stopped Admirals alone.
Mid level commanders like Izo + Fossa + Jiru + Haruta + Namur + Kingdew + Blenheim passed through Admiral Kizaru and they said 1 Admiral can't stop them when they work as a team.
Mid level Yonko commander Rakuyo attacked Kizaru and didn't lose.
If Admirals have problem with Yonko underlings, how can an objective person believe the Marines can match 4 Yonko and their underlings at the same time. Even if a miracle happens and 3 Admirals + 1 FA individually matches with healthy 4 Yonkos who won't have heart attacks, who will match with Yonko underlings like Marco, Jozu, Vista, Beckman, Katakuri, Cracker, Smoothie, King, Queen and Jack?
Vice-admirals can't even match with mid tier YCs like Daifuku, Oven, Snack, Whos who, X-Drake etc. They would get fodderized by top commanders. Even Shichibukai can't save them. Mihawk couldn't pass Jozu, Doflamingo loses to any top commander like Marco or Beckman or Katakuri. 4 Yonko steamrolls Marines + Shichibukai if they fight.
If Marines + Shichibukai still had advantage against 2 Yonko, they wouldn't stop fighting when 4 billion bounty Yonko Shanks came to stop the war when they had still trouble with Marco + non-Yonko BB.
Jimbei joined the shichibukai 11 years ago.
Shanks became a yonko 6 years ago.
/thread
Shichibukai were established before 4 Yonko with Shanks joining the 3 Yonko or someone was Yonko before Shanks and Shanks dethroned that previous Yonko which is a low possibility.
Marines already begging help from Shichibukai against 3 Yonko (unless you believe there is another Yonko before Shanks).