Thanks for the chapter!
MC really needs to learn some common sense.  That and what magic is considered average, midgrade, and strong.  As for the others' mission they were suppose to solve the cause of the creepy voice at night, didn't say anything about extermination.  After all, if it turned out to be a guy who got some money, is depressed, and so was getting drunk every night while moaning his woes it wouldn't be mission complete if they killed him but murder.  Rather than deciding failed it themselves they should just report to the guild that a dark blob hiding in one of the ditches was the source of the noise and that Lex killed it.  Granted they didn't kill the dark blob, which is probably a higher ranked extermination request than the level of the quest they had, but they did find out the cause of the noise so at least shouldn't be considered a failed quest even if don't get paid for solving it themselves.