I know it wasn't this chapter but I thought of it while reading this chapter...
Why did the humans send the heros as disposable fodder? You could fake the summoning and use a couple of peasents if you had too if it was all for a ruse or Summon heros get them achievments then sends decoys as how the story played out then you get to keep 3 people whom are as strong as an army of normal people.
I think one of the key things, may be that by bringing people from somewhere else, they don't have any guilt for their possible (and likely) deaths. They aren't citizens with family in this world. No one to get revenge on you for using them.
Otherwise, one could have some random Jane or Joe, "make a deal with the devil" with the king, and have them set up fake heroes. That may be a fun story, which I don't know if I've seen before. Usually, characters in that role are the villains, or working with the real heroes.