I see it like this, don't know if it's valid. Think so though:
The weapons the GTA fired in the first war against the Lucifer were all pulse based. This can be compared to throwing pebbles at a resistant surface of liquid (let's say a jelly or glue) with a target 10 feet deep. The pebbles with your human strenght will not reach the bottom, they penetrate the jelly only so far but the tension at one point keeps the pebble from reaching it's target, besides it starts losing velocity at some point when thrown. And since you are only allowed to use your hands and no tools, you cannot simply shoot the pebbles into the jelly: you have a limit of force you can practise on that surface with your pebble. No matter how many people throw at once.
The beam-weapons the GTVA fired at ships are continuous. This can be compared to holding a stick in your hand and pushing it down at that same resistant surface of liquid or jelly. Since you can keep applying continuous presure on the stick at one end you can push through the jelly at a slow pace, eventually reaching the bottom 10 feet deep. It'll be more difficult as the jelly resists, but eventually you'll win out with enough strenght. Even if one stick won't do, you can use another stick in your second hand, or get 20 people to press with sticks near yours so that the jelly can't resist all that concentrated presure.
So beam weapons, if plenty, would probably penetrate that Lucifer shielding, rendering it obsolete.