Realistically speaking, Royal World Spirit Master are grand figures Primal Soverigen grandmasters heavily rely on. They could forge pills, weapons, or any other kind of Martial resource that can cause grandmasters of cultivation to go green with envy.
Being able to reach this high class of Spirit energy Laws of course means that the World Spirit Master's prowess is equally immense.
Even a Holy King Master needs to tread carefully around 4th Class World Spirit Masters. If not, they would risk offending a dangerous figure who can escape from their grasp and show up later with more powerful forces.
It is indeed true that most of the time, World Spirit Master's raw power output is sometimes lower than Martial cultivators. The Law principles within an Inner World can suppress some paths of Spirit energy.
However, it was only some paths.