Well, if Cameo is right and Lalo has Ryuusei's vest too, they're already in a stalemate; there's no way for Baku to become the Kaiser in one day. If Lalo just had Arata's, Baku could still get lucky and not have Arata become a king during the allocation. With Ryuusei's vest captured, at least one of Ryuusei/Arata is guaranteed to become a king, and Baku will be unable to unify the island as Kaiser. Meaning they would both lose. Lalo's plan is likely to force a stalemate and have a 1v1 gamble with Baku for the entire match.