Since the flesh of the undead dragons had been stripped away in life, leaving nothing but an empty skeleton frame, the powerful strength of the Dragon Race could not be manifested in the undead dragons.
The Soul Fire of the Bone Dragons was formed by sacrificing an advanced undead, and is not the original dragon soul. Essentially, Bone Dragons are just a special type of skeleton.
And for the Ghost Dragons, their Soul Fire was transformed from the dragon soul, but for ease of control, almost all memories of the Ghost Dragons' previous lives were erased. In other words, Ghost Dragons lost the inheritance of the Dragon Race.
So, during battle, Bone Dragons rely on their Hardened Dragon Bones infected with Death Qi, while Ghost Dragons retain some of their instinctive close-combat abilities from their previous life, in addition to some abilities common to undead creatures.
