Wych Cult does not work.
Impalers have a base crit chance of 70%. With Wych Cult they still have 70% crit chance.
Additionally, this upgrade is extremely weak and should be much higher than 10% to be useful. Even if it worked, it would still be useless. 10% crit chance means LCs effectively do 0.1 more troop damage per Impaler, and BBs do 0.3 more troop damage per Impaler--absolutely not worth an upgrade slot.