After Han Fei became an Explorer, he felt more and more that spiritual energy was a bit useless.
Considering there was an upper limit of his capacity for spiritual energy, it was even more useless.
In fact, the amount of spiritual energy a human body could accommodate was always limited. Even a Venerable couldn't force a massive amount of spiritual energy into his body. Even if he could, it was the result of compression. Fortunately, he had the Demon Purification Pot, which allowed him to use infinite spiritual energy.
After he became a Venerable, the utilization of spiritual energy became even more slow. It wasn't an overstatement to say that Han Fei felt that he was like a person who was used to driving a supercar forced to drive an ox cart.
To be honest, he didn't feel that the utilization of spiritual energy was slow before! Why did it slow down after he became a Venerable?