Why is the 9 tails such a threat?
How big/powerful are giants/lil Oars in One Piece?
I personally do not believe Madara/karuma is a bigger threat Hashirama.
Because.... Kurama can spam a dozen TBBs, each of them being at least x5 more powerful than a typical TBB (with is easily a mountain level+ itself) ; all of that mounting up to solid island-level firepower. Firepower that completely shits on whatever OPverse has dished out.
But the thing is they can be easily countered/blocked/deflected. It does not matter if they can produce an attack with a bigger area of effect as it it can be countered.
There's no one on the OP side that can do anything to defend against a TBB once it explodes. And even if BB somehow manages to absorb a TBB prior to its explosion, the Op side have absolutely no defense against Madara's shockwaves. Shockwaves that are capable of two-shotting, if not one-shotting them.