A) Energy is energy
B) If the gun that Unit 01 used REALLY did fire Positrons then Earth had no atmosphere. Why? Because, a positron is a particle of antimatter, and if it came into contact with a decent ammount of matter (say, the air between Unit 01 and the angel) then we could kiss Japan goodbye. Since Japan is still there at the end of the episode, we can assume that the techies made a typo and the gun, thankfully, did not shoot antimatter particles. Either that, or Earth's atmosphere had disspaited away and all life on the planet had ceased.
C) "You need progressive weapons, positron beams, or just a large, sinking battleship"
D) Assuming Wing Zero is made out of the same material that the cable spool/carrier deck is made out of in the above referenced episode of EVA, then it's indestructable.
E) Who cares?