Some really interesting points! I'm starting to build a new Cities army and wanted to lean into a pseudo Devoted of Sigmar army. Phoenicium seemed like quite a good choice flavour-wise, but there don't seem to be any decent army-wide buffs and as stated above seems more about forcing your opponent's hand.
The smattering of battle reports I've seen online seem to favour running it as a tanky army and any death-related bonuses are just nice to have. Perhaps that's the way its supposed to work?