Having read through the whole thing mostly out of morbid curiosity, I have to agree with the translator that this doesn't really work. First off the lolicon element is gross, and there's a lot of it. The MC is beyond pathetic, and manages to be unsympathetic by not being sufficiently resistant to the idea of being the forced lover of this loli creature but instead seeming willing to go along with the sexual aspect which makes him deserve all the shit that happens to him. Since he deserves it, it's not funny. Funny would be if he's pure and innocent and only wants a genuine love with the girl his own age he has a crush on but everything goes horribly and ridiculously wrong to him and he suffers undeservedly anyhow. Comedy often comes from subverting the common sense of a familiar situation, so having the innocent punished contrary to what we would think of as karma is funny if played over the top enough. Instead, what we get is a bad person being hurt by a worse person and it's just dull.
Read or watch Bludgeoning Angel Dokuru-chan instead, it's similar to what this is trying to do but is far funnier.
1. Because as it seems, the enemy doesn't have much armor anyway. And they do use meat shields (at least Barak does, the others might just not strong enough to lift a full grown man in armor) 2. Probably because they are lacking in provisions. Like what MC said the first time he arrived at the base? Or like Zen said, "They are dumb" 3. We still don't know the layout of the battlefield, so it's a bir premature to say they didn't. Maybe the bowmen are protected from far in the back? I can see the boss talking so closely with the gunner, and I doubt the boss will want to go to the front