Just a few brief comments, I don't have time to respond to all of this:
You're good to not include Mjarin as a Leveller, because he wasn't. Myth 3 is not canon.
The Trow never fought for the Leveller willingly. In fact, it's explicitly stated that they fought *against* the Myrkridia (except in Myth 3, which is again, not canon), and that they served Balor because they owed him their lives, *despite* his being the Leveller (i.e. otherwise they'd have told him to go fsck himself).
The Ghols were originally conceived of as undead. In fact the Trow were supposed to be undead too. The original version of the story, from which the spinning-coin theory comes, was straight up undead-versus-living, switching every 500 years. That's clearly not so anymore; the Leveller just causes "darkness" by whatever means, be it predominantly undead as Balor used, or predominantly living as Moagim used (the Myrkridia). I imagine Moagim used some assorted undead as well (probably had the Watcher on his side), just as Balor used some assorted living (like the Ghols).
My old Principia Mythica theory (which I still want to make a scenario out of, damnit! At least one map! Maybe I should just write a story about it) has the Ghols as Dark/Old/Spider-God worshippers, but still technically a younger race.
Um... I think that's about it. Yeah. Dammit now you got me thinking about my theory...
