The reason Benack, a relative of the king, was stationed at the dueling grounds, was that the king wanted him to use this chance to train his swordsmanship with the slaves so that he could be of some actual use. It was a shame that the king's effort was wasted. During Benack's first duel with a two-star-gold-ranked slave fighter, while he did manage to wound his opponent heavily, he had his ear bitten off when the slave finally managed to lock him down in close combat.
In the end, the gold-ranked slave was cut into mincemeat and fed to the magic beasts. However, Blademaster Benack, who had barely escaped with his life, never dared to use gold-ranked slaves for training ever again. He only sparred against silver or iron ranks to bolster his confidence. Jiluet had warned him before that training against someone of vastly inferior abilities was of no aid to one's swordsmanship, but Benack did not care about his advice at all and tortured the low-ranked slave fighters to death to satisfy his twisted desires.
Blademaster Benack was a rank 1 blademaster who had relied on precious medicines and supplements to attain his current strength. It is understandable that he might not be able to fight against a desperate gold-ranked fighter.
Benack' relied on outside sources to improve. Usually, it meant that the person in question would not be able to improve much further. Benack would stay a rank 1 blademaster for the rest of his life and would always be inferior to those of the same rank that broke through naturally.