Where did you get that ACoC is not a sword skill? It is skill requirement for top tiers. Top tier swordsman like Roger, Shanks have this skill, it is this skill which makes them top tier swordsman. A stronger swordsman than the ones mentioned has stronger skill than them too.
Swordsmanship encompasses all haki, if your haki is weak your swords will break, you will lose the clash and get killed. If you cannot perceive the attack you wil not be able to block/parry/dodge it and you will get killed. Swordsmanship requires the highest levels of haki of all types because one mistake, one attack is all that is need to decide the winner.
That was intermediate CoC
Swordsmanship encompasses all haki, if your haki is weak your swords will break, you will lose the clash and get killed. If you cannot perceive the attack you wil not be able to block/parry/dodge it and you will get killed. Swordsmanship requires the highest levels of haki of all types because one mistake, one attack is all that is need to decide the winner.
That was intermediate CoC
As long as your Sword is CoA hardened, it won't break..
Intermediate CoC or whatever, it was still an island CoC level feat.. Zoro will never reach that..