The Zoro hype is real but you also have to realize this the classic Shounen 'Power-up with a physical toll' trope. Even though he fought it off the sword was eating his arm from a simple slash, when he gets into an actual swordfight that thing is going to fukk him all the way up.
Brah chill, you gotta realize we're talking about the GOAT ZORO
AKA Mr slices up fish men under water
AKA Mr
AKA Mr sliced up a god damn castle and he wasnt even trying
aka Mr cut up a dragon in mid air