I know the manga you are referring. It's just the author, slowing down the story progression. I can overlook not figuring out a way to communicate with the animals as his thinking is still constraint to our world. But like you said, the demi humans exposes this issue.
It's seem like it, but if the king still had his magic stone intact, it would have taken more time. He has been in power for so long and would have not let it happen without everything he got. The results could also be more devastating.