how would everyone in the alliance retreat? and wouldn't that extend too much?
That is the point only the worth people would get saved as the Strawhats,Kid pirates,Marco,some Minks and few other people. However the rest would get caught as I said. Then we would get a second execution scene where the rest of the alliance(Scabbards and co) who couldn't escape,prepared for their death.
In that case do you remeber when Kaido said that pirates would always flee when they where losing? Scabbards spirit broken, they don't having any hope anymore,whole wano in chaos, many people get died. The whole country spirit would be gone,pirates take the captial under their control and in that moment a pirate who even face losing would come back to save anyone for the last battle. The perfect tension for a all out battle.
and wouldn't that extend too much?
If we end the act 3 in 5-10 chapters, making a switch 2-3 chapter around the world and starting act 4 for 30-40chapters in a full war. Why not?