The main point of adding shootdown early on, is so that you can familiarize yourself with it (even if it's weak/near useless) and it's also so that you can unlock relaunch.
You SHOULD NOT add double strike, why the hell max it when even you admit it's weak? I don't even want to use it even if i have a sp reset because of the mana drain.
SP points are precious in this game, so keep the sp that your going to invest in doubleshot for your 2nd job skills.
And lastly, bow mastery's damage isn't that significant (+15 when max if i recall correctly, i'll check when my client finish downloading) and i feel that it's a waste of sp.
But anyway i can't proof telecast right or wrong in the "You level faster aspect" It is true that you Do more damage per second (bow mastery adds damage, an additional skill, adds damage, skill spam)
You won't be able to build your combo count as easily.
Anyway in CBT, your given a free skill reset for lv 1~19, It is not confirmed if it will be carried over to OBT.
Do not add double shot IF you do not have a skill reset. else, feel free to experiment for yourself.
Why do we even have moonwalk anyway? you still can be whacked to death in pvp when your using it.
moonwalk+moonwalk shot= near useless.