-They can fool humans, but not divines/demons. They see right through it. Illusion magic hasn't been created yet, as it is useless to them, as they are constantly battling each other and can sense an enemy source of magic right away.
-Fallen Azurin are very rare, you can count them with one hand. Angels are very proud and the overwhelming majority are very good and kind. So, fallen ones will be bosses/hidden bosses at best.
-Yes, exile is more of a test. To see what the fallen azurin will do with their free will. If he continues to be good and kind like the Soaring Heaven essence is, they will be allowed back. If they turn neutral/indifferent or evil, they will continue locked out.
-Healing is one thing, draining is another. You can't heal a soul that is being literally eaten away. When I say healing, I mean closing a wound or restoring a lost memory. You only have one soul. If that's gone, the person dies.