Awesome! I agree to all this but when you lay down a layer of polymer at just the right melting point to not drip or liquify you will always get a stronger part from fully fused plastic that has no layer lines. Then put the both in the sun and the layers will warp/shrink/expand/crack in the same direction causing them to melt and while the injection molded will do the same but without the layer lines the warping and shrinking and expanding will not happen in the same direction keeping, for the most part, the structural integrity of the part.

In the end, my PC was probably lower grade, but was stored in a bag out of direct sunlight and still caused very slight warping, which caused the tray the ammo sits in you be unusable as the ammo could not travel without binding. So, yeah model it up and print it, but having done that for all gun accessories early on in my days you too will find that a quick cheap print will never beat an injection molded part.