The first time big mom used ikoku she cut King Baum with it. You seriously need to stop coping . Shanks is a swordsman . He’s using adv Coc on his blade and swing it just like zoro . There’s no mystery here
It's no surprise Shanks's offense shits on the likes of Big Mom or even Kaido for that matter. Shanks is an offense-centric fighter while Kaido and Big Mom are more defensive types. Shanks's offense is much better than the Rocks duo just like how their defensive prowess like endurance, durability, etc, shits on that of Shanks. With that being said, it's obvious Shanks is stronger than Big Mom, but this chapter isn't enough to put him over Kaido, period. Kaido's still number 1.
There was no sneak attack. Shanks jumped in front of Kid and Kid even said « red hair » before Shanks used Kamusari. Did Kaido sneak attack Luffy in part 1 because he failed to react to Thunder Bagua ?