There were enormous guardian dragons that seemed to be made or living in each of the Valkines, that's true.

They said they existed to prevent misuse of the eleth.

[As to the elimination of eleth...]

There was a being who was able to absorb all the eleth from the Valkines. They became dead and lifeless.

Left uninterrupted, that being may have been able to absorb all eleth in the planet.