I'm really glad you limit tested this, because i love seeing the non battle magic lores get some use. And i really like your choice of demon prince and greater demon. Really interesting game, and some VERY surprising combat results.
I'd take triple Sun Dragon (Noble/Noble/Archmage) over an Archmage and 3 Nobles on Griffon! Are either amazing? No, but the output from even a Sun Dragon is significantly ahead of a Griffon (no bite attack so it's all at AP-2, and d6 AP-2 stomps instead of D3 with no AP
I love the list. Very similar to what I took to CCBB. Did pretty well there and now taking an updated version to SBOT. I don’t think the flamers would benefit from the -1 to hit from the corona upgrade since it applied to the character and doesn’t specify the unit. I would be happy if it was different though.
You mentioned at the end about running either lord of change or keeper of secrets. I still prefer BT over them as he’s WS10 meaning most infantry is hitting him 5s or lords on dragons are hitting on 4s. It’s a bit of extra defense as well, he’s the only one that can really get a normal ward save and wear armour. I find arcane urgency is a must with him since he can be easily kitted. I do like the keeper and lord of change. Used both earlier on in the edition but both would die to anything with magical attacks. Felt bad to die to some smaller things. Had the bird die to a unit of brett archers with a damsel.