If you look at the characteristics, the black dragon and the ancient beast are comparable.
Characteristics: black dragon; ancient beast; Archangel.
Attack: 25; 19; 30
Defense: 25; 19; 30
Health: 300; 300; 250
Damage: 40-50; 30-50; 50
Speed: 15 (flying); 9; 18 (flying)
As you can see, besides the amount of HP, Archangels surpass both ancient beasts and black dragons in all other characteristics.
