Shadow pip rating should be merged into the archmastery stat. When you click the school icon (during battle or deck set-up) that allows you to select which school pips to generate, Shadow should be one of the options (except for lower levels who haven't unlocked the Shadow school yet). Any gear item that increases your shadow pip rating can instead be changed to increase your archmastery rating.
There are in my opinion too many stats to focus on and consolidation is desperately needed. This can be seen with the removal of shadow pip rating from Aeon and Merciless gear, which is extremely frustrating and IMO makes it a waste of time to farm this gear. There is no point in having higher damage and critical if you can't cast the spells that you want to.
