In the same vein as Beasts of Tashnar.
- gives them a unique role as a RoR
- thematic as in: "the biggest and baddest" lions hunt the bigger prey
- synergizes with the playstyle where they are used to block and surround SE's given that they are a fast unit with decent mass
- synergizes with their active ability that reduces the speed of enemy units making the above use case even better
- makes them a "good on paper" anti-skirmish unit with missile ressist, slow and anti-large
Last part is debatable because of how skirmish mode works - 8 spd difference is enough to kite a chasing unit into oblivion, so the HE player has to catch the units with proper positioning or some helping like Shadow magic.