Conjectures of their application aside, dexterity means the ability to aim and successfully hit a target, whereas the specific weapons skills (projectile, heavy projectile, etc) determines your ability to actually use weapons of varying complexity.
The difference is thus the handling of a weapon, and having the hand-eye coordination of hitting your target.
I want to reiterate my explanation in no way is a reflection or current or future skills-based rules. My explanation is only is actual practical definitions as they exist in real world/rp environments.
That said, perception would not replace my two other definitions as "perception" is the ability to visually or otherwise sensually perceive the environment one is in.