I think it's supposed to be that an age is Dark or Light in succession, and that is what is meant by "the Dark wins" or "the Light wins". Moagim the First "won" at the start of the Wind Age, even though he was captured, drawn and quartered... the Dark still prevailed for a thousand years.
Just because Balor and Soulblighter are dead doesn't mean they didn't succeed. Pyrrhus would be proud.
(And I think M2 would have been much better if Tharsis had exploded with Alric and his forces in it, killing them all and leaving the world dark and leaderless, but not destroyed).