If you’re playing on a character with high evasion the piercing debuff from cross guard (Highlander C1) will never be applied since the check for evasion is preformed prior to the check for block.
If we applied the debuff to targets that were also evaded during cross guard it would add some group utility to highlanders skill set allowing them to debuff for other piercing attacks. As well as make the skill at least useful for high crit rate or high evasion builds.