There is a marksmanship skill, not gun skill. It helps minorly with sights, be it on a bow, a pistol, or a sniper rifle. Frankly, most of it’s effect is on gun modding and crafting, not shooting.
That’s more an artifact of dividing them by damage type instead of dividing them by handedness. Had they been divided into one & two-handed, with perhaps pole and/or light on top of that, we’d still have about the same number of skills, just divided differently.
The gun skills also suffer from it’s own odd artifacts, like repeating crossbows and SMGs, or weapon mods letting you blur the lines between weapon types.