Hmmm the scenario is wrong
But the idea here is that you don't need something with rapid fire if it takes 1-2 seconds of burst shooting before putting it out of commission. The scenario calls for the Silver Gospel to take down unit after unit with 1 hit each.
The energy that was developed in the 2nd shift is compacted and used more efficiently for powerful individual shots. Imagine it being a ranged Yukihira Niigata. The buster shot is inexplicably more powerful. using 2 wing modules to form the buster can cut through a marine fleet and probably a few dozen feet of ocean. 4 wing modules combined is basically the ridiculously powerful cannon of Gundam X