One thing that seems to be missed is that his morality was challenged too. One reason someone could have to remain F rank while clearly overpowered could be to go in party of low levels to kill them. What was also validated is that he's not that kind of guy.
I my opinion, S rankers go beyond the...
In the french roleplaying community we have a say for people who contradict the DM too much : "TGCM" (Ta Gueule C'est Magique) which would translate to "Shut up, it's magic".
I think it applies well here ^^