If the BMP were supposed to appear in this battle, they should have appeared by now.
If Oda brings them into the picture only now, it will look actually kinda ridiculous, I think.
It will just be a boring back and forth from outside forces to artificially swing the battle into one side's favor...
They beating each other to stablish dominance is one thing. Totalmente legit by their standards. Killing Drake since he was a spy also.
But killing Jack just because, in the Middle of a war. Seems really poor decision making.