Heya, fresh lv50 and I was wondering, how important is it to get Mercy Strike (MRD 26 iirc) and most importantly, Stoneskin from CNJ 34?

Right now I have 8 in MRD and 15 in CNJ, and given my farming needs in philosophers and stuff like that I need to prioritize stuff. So for the current content I'll be farming (mostly wanderers for now for 2-3 more DL pieces I guess), is stoneskin really needed and should it be a top priority?