With many of the other FF villains, they usually had enough power to destroy the world. I mean, Sephiroth had about half the planet's power with Lifestream. But Xemnas had extreme power on a universal scale, as compared to a single planet such as Sephiroth or Kuja.

Also, there is no concept of death in KH. At all. There goes MEODP.

Ctrl + F "death" in the following link for proof.
Director Interview – KH3 Details from BBS Ultimania (Complete) « HEARTSTATION.ORG