That's the only scenario Alliance loses
You think calamities + flyers can beat Luffy Kidd Law denjiro Ashura dukes kawa Zoro Sanji jinbei ?
It takes an army to beat Luffy/kidd or Yonko themselves.
Lemme remind you BMP defeated Luffy/alliance many times in battles :
*Enraged Army handed Luffy an L
*At tea party Germa-Strawhat-firetank alliance got the quickest L ever in the manga. Tomato box saved them.
*Pero handed Pedro Brook Chopper Ls
*Oven beat Pekoms
* pre FS, he lost a round, run away from Kata.
* Fishmen-Germa - Strawhat Alliance got crushed... even if they escaped, they were already losing to Smoothie-Daifuku-Snack-Oven fleets way before BM showed up . ( Even Jinbei said he was treating his men when they escaped)
Beast pirates have only beaten Luffy/Kidd or alliance once :
Kidd / Luffy lost to Kaido.
In direct war or battle, alliance at WCI didnt beat BMP! Luffy beat 2 Commanders + Germa defeated those fodder sonz and his 10K chess soldiers, jinbei beat Opera.
The others didnt beat anyone else and never won at Tea party or Cacao.