Barrage has a duration of over 50 seconds, I generally fire off my combos before firing it so their timers can start refreshing. (I also prebuff it when applicable)
Shadowbind/Piercing's damage versus many mobs (with lower defense like the DD/Mage Moogles) is so comparable to that of light shot, that it does not seem worth the extra time spent in animation to use the combo other than to bind, or when fighting high defense bosses only.
I don't know how much Bloodletter's DoT and endgame proc do exactly, but if it is anything significant I wouldn't overwrite it but instead have your archers alternate their combo rotation.
Though Bloodletter does a noticeable amount of damage again especially on high defense mobs, the difference diminishes between it and heavy/light shot on others with less defense. If you are only concerned about your own damage then the small difference it will make to not simply change the orders of your combo at the start (sacrificing maybe at most one less bloodletter in the entire fight? Or more likely 1/3rd or 1/2 of your timer on one bloodletter) might be a good idea.
However, you should consider the damage your group is losing out on by your playing with blinders on trying to get that meaningless #1 spot in the parse results.
edit: de-barbed (sorry it is late as I am writing this)