the guns in fallout 4 were a larger symptom of Bethesda wanting to take fallout into their style and vision.
fallout 3 was them acknowledging it wasn't their original work and did, I'd say, a c+ job trying to copy fallout 1/2 style into a 3d environment (I am not talking about the story or writing, purely visual worldspace).
fallout 4 was them seeing the success of 3 as a go ahead to take the property in any direction they wanted and to them that meant double down on what they thought was popular in 3/wanted to do anyway.
fallout 4 has a bizarre visual styling to it, falling into an 1920s/-30s vibe when you look at certain weapons, props, and location layouts.
Fallout 3 at least did a fairly ok job communicating that its the future. safes had keypads as an example. In 4, the safes have very odd and outdated wheel style locks.
This is one of many strange decisions to make 4 into more of a noir era setting. Was it done because Boston? the mafia? H.P. Lovecraft? I am unsure as to why these choices were made.
It makes 4's visual presentation consistent aesthetically but not logically.
Why does a nuclear powered society still have the mechanical trappings of an era that precedes even the most generous spectrum of time the fallout universe uses to justify its other tech contrivances?
the weapons are what people notice because combat is 4's only focus for many people and the guns are bad.
I'd like 4's assault rifle far more if there were an actually logical looking gun present, like the fallout 3 assault rifle. The fallout 3 assault rifle accomplished 3 things.
1. Pays homage to the assault rifle from fallout 1 by being a wood and steel gun with a 24 round mag.
2. Gives the US military, somewhat in focus due to the location of DC, a believable infantry weapon as a counter part to the equally OK chinese assault rifle.
3. Provides a little lore backstory in its entry in the BoS terminal.
There is care in the implementation of something as small as a weapon in fallout 3.
In contrast, when the most someone can learn about the fallout 4 assault rifle is found in the art book and not inferenced from appearance, relation to a real world gun or past series gun, or found in a lore dump terminal/holotape, it highlights that the lack of care towards player expectations and a lack of respect for the world its placed in.