The item’s text reads that it boosts Weapon Mastery damage (e.g., 140%-160%), but it actually applies the old version’s values, resulting in a damage reduction, equipping the weapon may cause your stats to display negative damage multipliers.
The weapon is supposed to convert Weapon Mastery skills into Core skills and remove their cooldowns. However, it often fails to eliminate the cooldown for skills like Steel Grasp and Iron Maelstrom, forcing you into a standard cooldown rotation with severely reduced damage.