Look at their skills

For example, the phantom sword's 1st skill increases the atk/hp of swords. Each weapon has this type of 1st skill for its corresponding type.
The 2nd skill is rush (L)/barrage (L), if at least 6 swords are equipped.
Ok, phantom sword wasn't the best example.

The spear's 2nd skill is assault (L)/defender (L), with a similar requirement. And so forth and so forth.
The equivalent of 2 L skills (except for the hammer being assault XL apparently), and they specify all attributes.