The black serpent leader had already been a First-stage Divine Warrior prior to the bloodline awakening. Thus, his improvement wouldn't be as huge as a Demigod or Transcendent achieving it.
Nevertheless, for a First-stage Divine Warrior to advance to Sixth-stage Divine Warrior in one go was nothing short of a miracle for the black serpents.
After all, their Black Serpent Bloodline had never been strong, to begin with. If it were, the black serpents wouldn't have needed to rely on the Golden Dragon Bloodline.
In fact, if they had not encountered the pure Golden Dragon Bloodline by chance and raised a few Demigod-rank life forms, their Black Serpent Clan would have never dominated the Western Sea.
Even the black serpent leader reaching First-stage Divine Warrior was considered a miracle.