[Read to the end!]
The reason why the humans were envied by the spirits so much was because of this, the beasts were closer to the physical world and were less talented in the transfer of spiritual power, while the dragons were closer to the ethereal world and had comparatively weaker bodies. It was only a small race that wasn't even among the superior factions, yet they had the gift of mutation.
Yes, to the spirits, the humans were a weird race that had a huge level of mutation that caused them to be able to have such a variety of humans. All spirits are born in the nether world, all concepts in the ethereal world, and all matter in the physical world.
Spirits have to walk a great distance to achieve the success of accepting the physical world's spiritual power to be able to affect matter, yet this little race was able to do so from the beginning, it had a great connection to the ethereal world, and some could even step into the nether world.