I call shenanigans. In the previous time-line, the redhead soloed the entire agency including the boss. He failed the first attempt (it was fudgy but the argument could be made that he was weakened by his fight with su-yeon) but even after getting cured and healed and getting help from su-yeon it was still a hard fought victory. I call shenanigans on that.
Secondly, I call it on the necessity of the fight. Su-yeon could've reduced him to ash at any time, and he was able to instantly cure the poison. So why dodge it and play along with an unnecessary fight? Just turn the scumlord into a burnt end of a brisket and as he twitches on the ground swearing vengeance yadayada just have the redhead behead him. Girlfriend saved, revenge gotten, ares taken over, plus one follower. Job done.