What about just considering a realistic demonic worldview. Consider:
- Why Lucifer killed Metatron.
- There is very little hard evidence in the setting that God actually exists.
- Kronos and Yves. What are they really? What does it say about the symphony that it needs both of them.
- Heaven is hardly a utopia. The triads are as bad a secret police as any on Earth. They even punish thought crime.
- Heaven claims that the talking monkeys are important, but seem perfectly willing to manipulate, lie to, and kill them.
- Death (the real one) is an Angel.
- Freedom is a demon
- Humans kill each other left and right over religous conflicts that were directly inspired by heaven.
- It's not hard to look at the symphony (and especially Destiny) as a machine to feed Heaven with Essence. Every thing else could easily be a lie.
As long as they don't care about what happens to humans (and really why should they, anymore than
you care what happens to ants) it should be very easy to cast the symphony itself as a giant con and the angels as dupes. Perhaps if Lucifer's goal is to remake creation into something equitable.