Lufasu wins because the male MC semi awakens the real Lufasu. Benet is actually even stronger than level 1000 (she's like 1500) because in order to catch up to Lufasu she broke the hard cap imposed on on all living beings in this world. The thing is that the real Lufasu is even higher level than that at her full real power, being something like over 4k (I don't remember the exact number). The partially awoken Lufasu could break her limit to level 2500 or so which allows her to beat Benet. Afterwards she gains a skill that allows her to break the 1k limit for short periods. There's even more spoiler reasoning for this if you wanna know more.