Ren Xiaosu understood the deal Sorcerer Melgor was referring to was for him to become his servant in exchange for not killing Zhang Jinglin.
Disregarding everything else, this sorcerer was probably overestimating himself if he thought he could kill Zhang Jinglin. As the sorcerers had not fought any wars with Fortress 178 in a long time, their impression of the Central Plains people's combat strength was likely still stuck at the time when they were normal people.
The sorcerer had said that Ren Xiaosu was stronger than all the gladiators in the entire nation of sorcerers. Thus, Ren Xiaosu roughly estimated that the strongest people in the Kingdom of Sorcerers probably had physical fitness equivalent to that of a T4 combatant. Compared to the Central Plains, it was far inferior.