I really don't know if it is a bug...someone with more exp/time might be able to test/ comment but to me Archery spec does not seem to affect dmg.
What I mean is that lets say you get your power shot at level 13. You don't get the next one until level 20. Even though you are speccing archery that whole time up to 20 your level 13 power shot never seems to increase in dmg. So by the time you are trying to exp on level 18 and 19 mobs your shots are doing inconsequential dmg. Also I see no difference in the arrow dmg types...slash/pierce/blunt all do the same dmg. One the things archers had was the ability to match damage type to mob vulnerability....this does not seem to be a thing here...at least so far at the low levels I have tried. For that matter I can't see why fire/cold etc arrows have a 7 sec shot time compared to 5 for blunt/slash/pierce? I mean all it is a dmg type difference and that does not seems to matter. So as you are leveling you are getting these new arrows that would will never use as the dmg type gives you no bonus and there a 7 sec fire time compared to 5.