Looking at the gunslinger makes me think that dexterity isn't really the best stat you use for a firearm. I've shot a bow and I've shot rifles plenty and they are just worlds apart in my mind. Pulling a bow is much more phsyical in drawing the bow and holding it steady where as firing a gun is very mental in managing your breathing and preparing to take the recoil. I suppose the same argument could be made for bows, especially crossbows. At the least it seems like there could be a feat to use Wisdom instead.
The main idea that brought this up was the grit system but my own ramblings make me concerned that having grit tied to your core stat rather than an extra one would make it too easy to superpower yourself. In addition, several of the deeds that say "apply your dexterity modifier" didnt make sense when i read them because it made it sound (to me) like your character is putting some ridiculous spin on the bullet by flicking their wrist rather than making a calm and level headed shot precisely where they want it.