From the very beginning, the mountain of Exp wasn't smooth like other small Exps. Seth has not dwelled on that but perceived that he can make it more rigid by feeding it energy.
Removing some Exp from it and feeding Clear Stone has weakened it further. If he had done it again, it would have broken and become smaller and their value as an almost continuous source of exp would reduce.
To anyone else, if they killed that monster, the exp will be Specific, maybe 1 million exp or more. Then they will use it to level their class up and their Personal Arms like Attire and artefacts.
To Seth, it was converted into Exp Mountain to serve as a foundation for a lord. This came to Seth intuitively.
Seth walked to the mountain and touched it. He felt a pull, and his Blood Aura Flower Pathways activated together with all his tattoos and halo.
The aura the 9-meter-tall mountain was sucking from Seth stopped, and everything was channelled through the pathway.