Sanji can already break GB's defence (the wood defence, not his Haki) via his flames.
Momo was confirmed to be a weaker Kaido (dragon form, that attack specifically).
On the other hand, this ofc doesn't mean anything (something like Sanji has a chance now).
So no, your theory makes no sense.
P.S: not saying GB won't be Sanji's Admiral rival, there are arguments for it. But this is not one of them.