Who do you think the Admirals lose too? And when in the story would it make sense?
Imo, the Final War is not a singular event. After Laugh Tale (when the other 3 Yonko potentially lose), Luffy will know what to do as PK and how to achieve his final dream.
1st part is New Marineford gets assaulted. They stand to guard Mariejois. Luffy fights Akainu, Zoro/Sanji fight Fuji/Ryo the rest of the crew fight Zodiac VAs and the like. Tons of allies will be present, but imo Kid and Law wont be relevant until thw WG side of things
2nd part is Mariejois and the proper endgame of the narrative. We know FI needs to be destroyed, and it seems Mariejois needs to also fall (i.e. Redline destroyed), so this is where you factor in the ancient weapons and the like.
I "still" think there is more to Shanks' side, but he should justifyably go down like Blackbeard at LT, unless something changes.
Tldr: 2 separate wars (3 if you consider the 4 Yonko fighting over One Piece).