Just one person was the primary reason they made it to S rank adventurers. Sure, they were fairly skilled, but being able to gain experience without the fear of dying is a massive advantage. The kingdom should have just hired Licht to bring more parties around to become S rank.
That kingdom had the perfect S rank making machine and they threw it away.
You can't fix stupid.
As an older brother myself I find this to be a very satisfying read.