Thanks captain obvious. Listen up. With every other power weapon you can use your melee while wielding it. Even with rocket launchers. Meaning that you can still make use of your passive melee skills, while using every other power weapon. The reason you can’t make use of your melee perks with a sword, is because it’s a melee weapon itself. Using the melee button swings your sword. In many cases this means you have lost access to the class skills, that actually make up your subclass skill tree. This, plus the fact that a sword can’t be used at range, make this the worst power weapon to use, by a huge margin. It’s the only power weapon that actually makes you play worse and get less kills, as a result. Get it?

Wise words