The reason why Zhao Hai wanted the hundred treasures world to attack the flame Weaver race with all their might was that he was afraid that the two worlds would be delayed. If it was just One World fighting the flame Weaver race, then both the hundred treasures world and the special Arts world would go all out.
However, if the two worlds were at peace, they might slack off. Humans were just that strange. If one person did one thing, he would be very focused. But if there were two people, then there might be a phenomenon of waiting.