Yeah they don't have enough men. Kaido is weakened already, jack is out, he will come back but will still be weakened as well.
But mom doesn't give a shit about the situation. And her crew isn't coming.
As you said the Tobi Roppo aren't really loyal to the crew. Even if they are the supernovas and some of the straw hats can take care of them.
2 calamities left, zoro and sanji will take them out.
Luffy will solo weakened kaido.
And the alliance still have Marco and Yamato who can basically sit in their asses.
Easy win for the alliance.
And you're also right, some of the scabbards should have stayed down, it would have made things even easier for them.