is it possable that like the leveller, there are other "kindred spirits" that sometimes acompany him. each of the spirits is a dark god in his ethereal form. and each one of them is chosen as leveller by random and is forced into the world to destroy all life. adn this leveller can ressurect the others to serve him.
for example. back with moagim I. he must have had generals. adn these generals were, Culwey, bahl'al and the faceless one.
these generals were the fallen lords. but in order to ressurrect them to the Leveller's cause, the leveller had to know one of the names that represented their spirit. the leveller would then ressurect the spirit through some other body and they would inherit the memories of that body, making it appear that the spirit was the person, gone bad. much the same as the way the Balor inherits Connahts hate for the Myrkridia.
this would explain the different names of all of the fallen lords. and the fallen lords would be the incarnations of the Dark gods, following the leveller. their true names known only by themselves and the ghols.
now. the reason that Myrdred was able to escape the power of the spirit controlling him, was that his willpower was strong enough that once the leveller was defeated, he pushed the dark spirit out of his body.
Shiver, after she was defeated, returned in myth 2 as Ravanna, and not the spirit, and Myrdred recognises this, being free of the spirit himself and calls her by her real name.
and soulblighter, although not dead was possessed in a weakened state of mind in his pursuit of immortality, and was called to the leveller's side. Soulblighter was the name of the spirit in Damas's body, but since he wasn't defeated, he kept the same name of the spirit. and remained evil. in the flavor text that states that the soulless were one of his most successful creations, it could be in line with what myth 3 was saying because, the soulblighter spirit under a different name, may have created a soulless in a previous age
and last. the Watcher. was still inhabited by the same spirit that had possesed the body of the ancient war hero, of the bre'unor, Bahl'al. he was never defeated in the previous age, and had grown to be the most powerful of all of the spirits, strong enough to survive an age of light, undefeated. he returned to the side of the leveller, adn he was defeated by fragments of his own bone.
these spirits have each been leveller at one point, and althoigh not always reincarnated, they still exist on the ethereal.
what made balor so powerful, was the fact that he knew all of the spirits to reincarnate, adn who to reincarnate them into.