Of course, what makes the Fire Emperor unwilling to truly expend all his power on matters of the sea domain is not only the threat from the Great Ming Divine Dynasty, but also because it is destined that the forces overseas cannot be forever controlled by them.
Originally, why did the Five Emperors' descendants divide into two branches, one in the Central Earth Continent and one overseas, if not to avoid putting all eggs in one basket, and also to maintain balance.
Don't think that the strong in the Transcendent World don't need balance. For emperors like the Five Emperors, balancing the power of their subordinates is almost an instinctual choice.
Even as Taoist Monarch strong as the Five Emperors, with supreme authority, if the people below group together to resist them, it would be extremely uncomfortable for the Five Emperors.