I agree with your first point, not because I think taking away the firepower is a problem but because I think the way the movie does it is odd. The Aliens are well established to have acid for blood, and they show several being absolutely blown to bits. Still only one guy in the main conflict gets a face full of 2020 Afc Eastern Division Buffalo Bills Champs National Football League Shirt. I think it would make more sense if they kept their firepower, only to realize that even if they killed the creatures swarming them they were still dying thanks to acid showers.
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