Rapier is not a light weapon, you can only dual wield with light weapons. Rapiers are actually kind of heavy (and long) They are a finesse weapon, but not light. IMO most 1handed swords in D&D are actually short swords.
This makes sense. It's a finesse weapon because of the accuracy you need even if it's heavier. Spear should be the same. You can wield it efficiently with just brute strength, or by accurate strikes hitting weak spots. But Pike is too heavy for such.
