Also, you all shouldn't underestimated the Heroes. While Heroes aren't all at the same level, the ones from the Kingdom would've been able to defeat Ogre Rou, and if they team up they would absolutely be able to beat and kill current Rou.
And these Heroes are not even the strongest ones in that continent by far.
For comparison, do you all remember the Insect Hero from the end of the Forest War arc? That Hero had very bad battle compatibility against Rou, and yet he was still able to fight a semi-serious Rou without needing to go all out. Furthermore, that Insect Hero is a Great Hero.
For clarification about the differences of Heroes and Great Heroes:
- Heroes are stronger individually and usually have a party of a few strong individuals.
- Great Heroes are more commander/general-type heroes who can command troops/summons while giving them lots of boosts, and these Great Heroes aren't as powerful as Heroes when it comes to individual fighting power.
-Legendary Heroes (like the Founder King Rorgis) have both traits (high individual power and a party of a few strong individuals) + (troops/support/buff powers).
In other words, the Insect Hero was able to fight a semi-serious Rou without needing to fight seriously even though he's not himself that powerful when it comes to individual combat as a Hero.
Also, all Heroes(regardless of type) have their own Book of Psalms like Rou. You don't need to be a Hero to have a Book of Psalms, but having it marks you as one of the "main characters" of the World, each being chosen people by different Gods of varying ranks. Rou's party in this case includes Kichi, Kanami, Asue, Sato, Sei, Ji and a few others from his group.