A Banished Failure Survives in the Borderland and Becomes an S-Rank Exorcist Chapter 30 Discussion

The premise isn't believable. MC survives 2 years in hell, becomes OP, returns and has the same timid personality with self-esteem issues as when he left. Doesn't even have PTSD. Then the story pulls a bait and switch and turns into a mu*der-mystery for some reason.