Isn't it called an act of Wano tho
If Onigashima is an arc as the third act, then the first two acts were also different arcs ?
Oda even took the time to show Pudding next to Big Mom when we see the shilouette of Big Mom in FI for the first time, but never hints at Yamato even though we got glimpses at Kaido multiple time since the end of Dressrosa.