As far as the laser debate goes, fallout has actually been better about portraying fairly realistic laser weapons than other sci-fi mediums, in the regards that they are a continuous, instantaneous beam. I already explained why fallout laser weapons aren't silent.
And the visibility of the beam is justfied via https://en.wikipedia.org/wiki/Rayleigh_scattering.
And like my argument, considering we are firing a beam powerful enough breach protective gear and kill a man, they'd easily have the intensity for rayleigh scattering to take effect.
While the concept of a "Microfusion Cell" is inherently unrealistic, it would probably take a portable fusion device or something of delivering an equivalent amount of power density to fuel a portable laser weapon with a cell the size of an 8.oz soda can.
Now to address how the weapons don't over heat or destroy themselves, well in previous titles, it can at least could be loosely explained away by that they do via item degeneration. Using ammo that makes your lasers deal more damage would destroy it faster, and "overclocked" weapons like father Elijahs Tesla cannon and LAER would wear out quickly. But in FO4, we have no such system.
The only truly "unrealistic" (or believable within the context of the setting as I like to put) is that they arbitrarily have recoil with no form of explanation be it groundings in actual physics like the stuff above or an in-universe justification.