Hmm, the reason 40k scale (and mechanics) is so wacky is because its based on Warhammer Fantasy.
I mean consider the max range for an ultra advanced gun is 24" (a few hundred feet tops irl) and that the round it fires has a similar impact of a melee attack. Makes no sense.
Then consider that in Fantasy a black powder rifle shoots 24" (in this case the range is realistic) and that it has a similar impact of getting stabbed with a sword...makes perfect sense.
40k was built over a foundation of a fantasy game along with rules simplification (everything moving/assaulting same speed 6") when you realize this the picture becomes more clear.