Beginner Gold Grade Pranic Beast—Empyrean Boar!
The reason they were called the weakest of all Gold Grade Pranic Beasts, weak to the extent even Silver Grade Pranic Beasts could kill them was entirely due to their Primary Nature.
Primary Nature—Voracious Nature!
When an Empyrean Boar wholly devours a Pranic Beast, it gains the Pranic Beast's Primary Nature. Originally, such an accumulation-type ability would have made them the strongest. But there was a problem here.
The ability they are accumulating wasn't a Skill but the Primary Natures of their targets.
A Primary Nature was a Pranic Beast's original state of being, one it adapted to specialise in after thousands of years of nonstop evolution. From the way it ate to the way it shat, everything was optimised for survival.