Rule Runes were more complex in practise than they were in theory.
One could simply define them as enablers; they removed the need to declare Rules verbally, as Jerthrax had done when he used them against Actuass, Replicus and the rest. This significantly reduced the time required to cast them, and even better, disallowed enemies from knowing the properties of the Rule being cast.
That said, Rule Runes were still in a tier of power higher than what Jerthrax had been able to attain. After all, they made it easier to conjure dramatically powerful influences that were unreachable for ordinary, high-tiered combatants.
This was how Jiggorrhax was able to conjure a world.
'Incredible!' Replicus thought.
To think such a feat was possible.