I love it. But I would go Eudaimon so no confuses it with Daemon aka Yugoloths (NG), Archons (LG), and Muses (CG), all Greek words. Let Angels just be direct servants of Gods (or Guilds in Ravnica).
Daemon (classical mythology) - Wikipedia
I think personal preference is bound to come into this sort of thing. I don’t much like the idea of an all Greek or even classically themed upper planes. What I was going for were terms that would be familiar in English and that have some resonance with the alignments they’re meant to represent. I was also thinking about how the lower planes were populated and how to create the same level of differentiation for the upper planes.
Devil and
demon are very natural and familiar in English, and
daemon, while less familiar, is an understandable choice, although I think
cacodaemon might have been more accurate. I dislike the change to
yugoloth and the other names for fiends that came in with 2E, although I note that it does free up the former term somewhat, which is why I suggested
daimon for NG celestials. The alternate spelling and pronunciation would provide at least some differentiation from demons/daemons, although maybe not enough.
Angel seems like the natural counterpoint to
devil, and the concept of abrahamic angels seems to fit well with the LG ethos of service, loyalty, and devotion.
Archon, on the other hand, is a Greek term for someone who holds the office of a king or, literally, a ruler. Now while the concept of rulership is tied in with how I’m conceiving of angels, I’m not sure how
archon is a more appropriate term to apply to spirits.
A muse, to me, is one of the nine goddesses that bear that name, which I would place above the typical denizens of the upper planes. I chose the word
genius because, even though it has other meanings in modern English, I feel it captures the concept of a personal tutelary spirit which I feel jibes well with the CG emphasis on the individual.
