Problem in final war, milhawk is not siding world governmen. Before final war start, zoro already defeat mihawk to become strongest swordman
Final War is much more complicated than you realize, it isn't just One Side vs WG Side
There will be tons of Reveals & Plot Twists & Characters switching sides
All Straw Hats dreams are Split in Two, reaching their Full Potential & then proving it
In other words:
Before Final War:
Zoro will reach WSS Level but he can't prove it till he Defeats Mihawk in Final War
Nami will learn about Geographical Mystery of the World, but can't Draw Map till Post-Final War
Usopp will become Brave Warrior & lead Elbaf Army but won't be known as such till he participates in Final War
Sanji will learn where is All Blue, but can't access it till they win Final War
Chopper will learn Secret to making Perfect Medicine but won't be able to produce it till Final War
Robin will learn most about True History but she will realize that she must find more Answers by going to Mary Geose
Franky will improve Thousand Sunny to make it Best Ship ever but it will be till Final War that he uses it
Brook will be closer to Laboon than ever (Since he will be on other side of Red Line), but can't meet it till after/during War
Jinbe will discover the True Enemy of Humans/Fishmen Racism but can't stop it till Final War
I believe that Straw Hats will realize Half their Dreams which is being "Ready" for it, when they reach Lodester Island, meaning End of their Journey around the World, however they will get the second Half of their Dreams only when they Participate in Final War