The skald skill sense weakness appears to be broken - at least according to the tool tips.
I had a full viking army and lvl 1 sense weakness which states it provides +3% critical chance instead provides a +6% bonus. This applied to all the units I had at the time (Warrior Maidens, Berzerkers, Jarls, Axe Throwers and Soothsayers).
However as if to compensate lvl 2 sense weakness (+5% crit chance) doesn't appear to do anything to the same units again working from tooltips.
I will update when I have pulled enough mind runes together to take tier 3.