Regarding phaser rifles, the scene in "Empok Nor" where Nog reports in toting a ST:FC style rifle when the security team carries the older TNG/DS9 rifle type makes me think the ST:FC design is not (merely/at all) newer, but somehow "heavier" than the TNG/DS9 "standard" type.
That is, there exists some reason why the ST:FC rifle hasn't superceded the TNG/DS9 style weapon, some difference between the two weapons. And the Nog thing would indicate that the ST:FC one is the "better" gun, at least according to the young Ferengi. Perhaps the "light machine gun" that only one or two people in a squad would carry to complement the more useful and certainly more compact "assault rifles"?
A squad from the E-E might also be equipped with, say, seven "standard" rifles and just one of these heavier things. It's just that the Borg in ST:FC were such an exceptional threat that Picard only broke out the heavy weapons and didn't bother with the regular ones...
The difference between the two ST:FC rifle types is something I'd very much like to overlook, considering Worf's gun suddenly and inexplicably switches from one model to another as he walks down a corridor. Since the difference between the two is an extra piece of plastic surrounding the barrel, perhaps this piece is removable in-universe - a "silencer" of some sort? The third rifle would of course defend its place in the universe by being a dedicated spacewalk weapon, with extra-clumsy handles for that extra-clumsy spacesuited grip; it may well be a "standard" rifle from the inside.