Because Luffy and Sanji decided to fight a BM defeat seems probable. An escape is unlikely now with the Tamatebako (seemingly) gone and someone busting in now would be a huge case of plot shield which should annoy most so that leaves the scenario of Luffy and co. fighting their way out.
I doubt Oda would have his MC come back after training with the PK's right hand, make a statement like "I'll never lose again" just to lose a few villains later. Plus if Luffy loses now then logically his story and journey would end because BM wouldn't let him live after this so if there's no more escape then the only option is victory.
How you can come to this conclusion after reading the last chapter is a mystery to me.
When everyone was fighting together, their defeat was imminent. But now somehow with less people on the Battlefield Luffy has a shot to take down Big Mom ?
Your entire post is filled with stuff that will set you up for disappointment in either the story, in Luffy or in Oda.
Because with Luffy there and the Vinsmoke family they have 7 fighters on their side. Against the entire Big Mom family. Even the fodders who were shooting have haki, as proven this chapter. Most Vinsmokes had to shield behind their raid suits while the top fighters didn't even make a move yet. Reiju got burned by Prometheus while her raid suit was supposed to be fire proof.
If you don't see how much of a problem that is than I don't know anymore. But I guess since you were underestimating Big Mom from the very start you're just going all in on it now and praying that Luffy will win by some kind of miracle.
As for the escape, you're also wrong there. 5 Vinsmokes have raid suits that enable them to fly, Sanji has sky walk and Luffy can fly with Gear 4th. There is also still the bomb at the bottom of the cake. We could see a self sacrifice of Judge to pay for his sins and have a new generation of Vinsmokes lead the kingdom in a better way and possibly joining the grand fleet.
But the amount of strong opponents verses allied members is like 3:1, and you still have an army of fodder unloading on you.
And to give a reason which is not story related as to why were not going to have a big fight. Oda confirmed both the start of the Reverie arc and Wano in 2017 at Jumpfiesta in December 2016. Seeing we're already half way through the year, I very much doubt this will be taking much longer.
If the Vinsmokes were strong enough to rival themselves with sweet commanders and Big Mom, why did they come for power to her for taking North Blue. They could've done that easily on their own.
