I will preface this post by saying I am in no way an Arc/TA expert. Infact, my highest Arc/TA toon is 17. I have looked at your build and what I can say, without ambiguity, is that I do not like the fact you did not take Flash Arrow. Flash Arrow is an awesome power. The reduced visibilty and -ToHit really helps. I cannot stress this enough, especially since it is a non-aggro attack. You lead off with Flash Arrow and pull, if you aren't lucky enough just to pull a portion of the mobs due to reduced visibility, the mobs you do pull will have their ability to do hit you reduced.
You also didn't take Poison Gas Arrow. I have no experience with this one in combat, as I haven't attained a free level to aquire it. However, with its listed status effect of -DMG, I cannot find a reason not to take it. This and Flash arrow alone are a great combination, expectantly. You reduce their chances of hitting you and when they can, they do reduced damage.
Like I said, I am by no means an expert. And if I have said anything that contradicts any in-practice experience you or others may have garnered, please disregard it.
