So, someone who knows more about ranged attack mechanics than I do can speak to this, but - since you should be pre-shooting in snapshot gear, and THEN changing to your "end the shot" gear with all your real ranged attack/+STR and such, isn't rapid shot just really making sure you shoot in your snapshot gear?
The increased shot speed vs. shooting in inferior gear seems like the real question.
So... your saying Snapshot is > Rapid Shot, because it gives delay enough to gear swap into ranged attack gear? And that Rapid Shot would be too quick for the swap?