Why is this saying to use abjurer merc with the Jitan barbarian only weapon in whcih it cannot equip?

Should I be using runes in all my gear instead of resist gems because of the skill that gives bonus per each rune?? does that work with merc runes also? WHich runes should I be using?? TY!

Anyone else have mana issues with this? im OOM in like 6 seconds