Fun facts!
1.The archangel of pain says "units inside 9 inches take a leadership test at -2 and suffer one wound for each point failed with no armor or cover saves allowed."
2.Soul fright is basically the same thing but without the -2 and on a single target.
3. With 2 HQs, one with armor or misery and another with the archangel of pain with a unit of any kind from the coven supplement means a unit would test leadership at -5 for the archangel and -3 for the TGL.
4. The chariot rule state.. "For purposes of characteristics test always us the rider's characteristics" this includes leadership.
5. Necron overlords are not fearless.
6. Since the chariot and rider are considered one model the rider doesn't get fearless for being embarked on a vehicle.
Verdict: you can archangel bomb/ PGL bomb a catacombs command barge.
Is this effective? Hell if in know! But I sure want to give it a try!!