I think you guys are selling the Strawhats and all a little short. let's look at the people who will fight Kaidou :
For sure :
Luffy and his crew
Law and his crew
Kin'emon and the other Red scabbards
The yakuza leaders
The minks
The rebel samurais
The Straw Hat Grand Fleet
Marco and the remnants of the WB Pirates
Jinbe, who will obviously return at some point in this arc
The Germa, who has unfinished business with Big Mom, even if only one or two surviving members
Possibly :
X Drake if he's the one helping Law
Hawkins if he foresees Kaido and Big Mom's defeat at the hands of the Alliance
Moria, if he's used to deal with the man who broke him, Kaidou
Weevil, if he stumbles in the fight - dumb as he is, he'll befriend Luffy when the latter will call him Whitebeard and says he look so much alike with Newgate
Added to that the fact that Big Mom's crew may not be at full force, since they only came with one ship, and apparently without Katakuri, whose presence hasn't been hinted at all so far, and while the Yonkou Alliance is extremely powerful, the Strawhats have a lot of powerhouses on their side. Inuarashi, Nekomamushi and Ashura Doji have all been able to fight equally with Jack, one of the strongest members of Kaidou's crew, after all.
Plus, there is the mystery of Rocks, who escaped Impel Down, if I remember right. He could go either way, since he saw what Luffy did to try and free his brother, I suspect.