Yes, this this this. The Giants, being old and powerful, intertwined with nature, the concepts of the world. They can't just grab "bravery" or "ambition" out of the air and stuff it into a rock, they take objects perceived as these concepts, a shield protects, thus it contains the concept of bravery, since the brave protect the weak, an old training sword, covered in abuse and age, holds the concept of hard work. Like you said, "old world magic" vibe, since an object that represents the concept would have to be old, having soaked in the concept for ages, the older it is, the stronger the concept is represented.
This is another important thing. Giant's wouldn't grant just anyone a weapon, or an item, forged by their hands, they understand how strong their objects are in human hands. They give them to the worthy, those that prove they can be trusted.
Another thing is the idea of normal Giant items being treated as incredible artifacts by simply being used by Giant's. Like gloves made by Giant's gift a human incredible strength, boots made by Giant's give a human who wears them a Giant's stride.