I also share @litregm 's opinion. Sin is not meant to be easy to level up, and its honestly not too bad as well. You have a lot of other ways to level which are less painful for a sin, questing, pq'ing fit a sin more, and its fine that grinding is a little bit harder on a sin. The change to avenger (hermit's mobbing skill) is very significant and will make your life easier on the 3rd job.