You do know that some character from sky island survived the same fall? Forgot his name.
Luffy can survive that fall too.
Bege thinks he can kill Bigmom with poison. Lol. Bege is not an accurate indicator.
This is the first time Bigmom spilled blood by attack. Kaidou spilled even for a mere stab from Kiku. Even counter shock from Law couldn't make Bigmom spill blood on the rooftop fight.
His name was Gadetsu, he fought Chopper on Skypiea. I know he fell from the sky, but we don't know the exact circumstances of his survival. We know know why Luffy and some other devils fruit users say logias, for example, can survive the fall. That's not the same reason why Kaido survived it. Kaido fell and took no damage because he was that durable.
I don't see why Bage's so wrong in thinking he can kill BM with poison; it was never proved to be impossible. Even Perospero thought it's possible as a matter of fact. I don't think we know her better than him. Also, I made it pretty clear Bage's assertion wasn't necessarily accurate, but it's a fact that Kaido, as of now, has far better durability feats than Big Mom. Be my guest if your only argument to say Big Mom is more durable because she's never damaged on panel while completely disregarding the fact that she lacks feats.
BM needed COA defense to match Kong Gun attack while Kaido took 100s of G4 hits with 0 resistance and took no damage. Big Mom's durability never got the same level of hype or feats as Kaido.