Unlike human beings and ordinary evil beasts, the Primordial Fierce Beasts are powerful living creatures that were born with much more talent than human beings. In primitive times, some Primordial Fierce Beasts that had evolved to the perfection were even on par with Innate Deities and Primordial Demons.
There were fewer varieties of Primordial Fierce Beasts in primitive times, but each variety had produced many famous and mighty living creatures. Not to mention others, at least at the beginning of their lives, the human being, who appeared much later, could not be compared to them.
Exactly because of this high starting point were there essential differences in practice between the Primordial Fierce Beasts' ones and humans' ones.