First things first—all of Heaven knows about the Exterminations. They see it as a good thing and a way of protecting themselves and the realm.

The Executionists are Throne Angels, while the Cherubs from Helluva are a Cherubim Angel (sharing one body). But given their role, they were only called down to Earth for an emergency and IMP makes them stay longer. They become fallen because of their poor handling of their rage and become wrathful—more specifically under God’s watch.

God exists here! Be it through mentions or his opposing voice that occasionally ruptures down. He watches the Earth, Adam and Eve watch the Heavens. Abel are their eyes in Heaven.

Given that Abel replaces Adam ( if I did follow the show’s format ) , his death is singlehandedly what causes Heaven to go into lockdown almost immediately.

Ironically enough, Angels are sexless / agender in a sense and are only feminine or masculine presenting.