[Why makes (the predatory blade/ damage 97-103) with a strong attack no damage? And with a normal attack only 73 damage like the blackice sword? Is that a bug or a the normal damage for a legendary weapon?]
I belive the heavy attack is intended, as the info says swing “madly” and swings more when you use light attacks.
Also this blade is now sweet for knocking out enemy if you put blunted fitting on it. R1 kill, R2 knock out
We can confirm that there’s no issue with the Predatory Blade and, as @Death-hunter1992 correctly states, the weapon’s info hints at how you’re supposed to use it, which is by swinging madly, and that would be through light attacks!