If you read more carefully, Oda already dropped the foreshadowing of Goroisei's weakness
Cursed / Kitetsu swords.
Zoro is shocked because he just sees Shodai Kitetsu which is higher quality than his Sandai, in the first time of their life.
Nusjuso is shocked not because he sees Sandai in first time, he is hundred years old he should have encountered other Kitetsu before. He is shocked because his weakness is in front of his eyes.