The logic in kiss tries to take into account picking up the most hurt mob. The assumption is that mezzed mobs won't be attacking so they should be less damaged. Damage shields and tank riposts should damage the mobs that are NOT mezzed.
The problem with knowing if a mob is mezzed or not requires you to target the mob. That could cause the MA to have to target every mob in camp. Also everyone in camp is assisting the MA so they will switch to the first mob he targets, so if there was an easier way to check, if a mob is mezzed without having to target the mob, we would have added that code a long time ago.