Well, we know that a particle cannons can pierce AT fields, and what are beam rifles if nothing but gigantic particle cannons?
And don't say "oh it took all the energy in Japan to do that".
Okay, I won't. The particle cannon only pierced Ramiel because of the synchronization between the particle cannon itself and Shogouki. The only thing proven to bypass an AT field is another AT field.
Long story short, bringing a Gundam to an Eva fight is like bringing a sword to a lightsabre duel. In other words it's like Soul Calibur IV; it just doesn't make sense.