They rather angered Kaido instead of risking for Luffy to awake his fruit. So they were more concerned for Nika.
Technically, they can be placed anywhere but don't act like them being last villains do not mean shit when the strongest top tiers have to fight them with Zoro, Law, Kidd, Sabo and Sanji at least. Confrontations between Dragon and one Gorosei is also possible.
Ofc this only counts if Saturn won't be defeated this arc but again, Luffy cannot beat Kizaru and Saturn at the same time. It's overkill and pure bullshit.