Avenging yasu doesnt mean killing orochi
yasu himself didnt think that
Yasus penultimate thoughts (his last being about toko his daughter)
are
NO ONE HAS BEEN ABLE TO TAKE KAIDOS HEAD FOR 20 YEARS
GO TO ONIGASHIMA AND AVENGE YOUR LORD
Yasu thinks to get revenge you go to onigashima not the flower capital to kill kaido not orochi.
and that is exactly what zoro is doing
Zoro is literally doing what yasu said to avenge him
Go to onigashima to kill kaido