Have you read isekai or other reincarnation stories that start with a summoning ritual and wondered why they always get some random layman from Earth? If the priestess and king are really summoning people from other worlds to fight the demon king shouldn't they get a being truly capable of taking the demon king down?

The Starmancer sat in his throne, watching the endless night sky. Another day studying the stars, waiting for a challenger to attempt to claim his throne. It's been about ten thousand years since he was born, and for the last five thousand of those, he had been the strongest being in the world.