That's right, the cultivation technique of the truth brush was indeed not as comprehensive as the true spirit world. Zhao Hai could clearly feel this because the cultivation technique of the truth brush had completely surpassed all the cultivation techniques of this plane.
Now, Zhao Hai could more or less understand why his thinking power could not keep up with the brush of truth. It was because the brush of truth came from a higher plane, which was why his thinking power could not keep up. This also allowed Zhao Hai to deduce the method to increase his thinking power, which was to ascend.
Zhao Hai had not noticed that Ascension could increase his ability to think. However, he had guessed it now. Although he had no way to verify this, he believed that his guess might be true.
Regardless, Zhao Hai knew that the mantra brush was an extremely powerful cultivation technique. Its most powerful aspect was not just its mantra's characteristics, but also its reasoning for the Dao.