Ive said 40 times already and you clearly are not reading and typing too fast:
- The Marines can join the war for the 4th Poneglyph against the 4 Yonko.
- It can be a massive free for all including fleets of every Yonko and other factions
- Zoro can fight Shiryu, Fuji and Mihawk, they will also fight each other.
- Luffy can fight Akainu, Blackbeard and Shanks, same deal
- Sanji to Ryo, Ben Beckman and Laffite
- etc etc etc for any other strawhat.
You are looking at this too narrowmindedly. Nothing says the Marines have to take part in the "final" war against the WG. You keep calling them the "biggest" military organization, yet Akainu has repeatedly stated that their issues are worldwide and they are spread too thin. The Egghead group likely will take heavy losses too, so no, the Marines do not have to be at full strength if they fight the Yonko. You can just have Akainu, the Admirals, Zodiac VAs and whomever else comprises of their remaining fleet.