I'm wondering what the Angel of death fight is all about to be honest... the messages and the whole "activation process" is kind of awkward and doesn't make sense to me. I mean what "Prototype"? Did the UAC build this thing or did they capture a demon and modified it? This all doesn't seem right to me!
The area you face the Aod in is also not really suited for such a fight... it's small and doesn't provide enough cover IMO.
I think the arena where you currently fight the cyberdemon would be a much, much better place to introduce this epic enemy!
Fully agreed, therefore considered as a bug.