If the hero is a Shaman, a Curator, or simply has decent defense stats (which is rare), the Executioner's "Cleave" ability is very effective. If you manage to accumulate at least two points of Rage, everyone will be trembling... and the "Aura of Terror" is simply amazing. We charge in with everyone attacking and reduce the enemy's defense by -3 (it's not effective against ranged units with high defense, as proven). So, there are options!
You're right, Executioners are better with high Rage, but Rage is an unstable stat. Sometimes you need to protect warriors like them, and to maintain a normal Rage level, you need to move around, which is extremely inconvenient when the enemy has a large number of archers.
