You can have a separate setup with Streak and cut BA to use the scamp, his damage is very correct and it prevents you to loose time to summon it before bosses (which is very valuable if your group goes fast).
This setup is in the context of a good group with Alkosh/Major Force/No sustain issues, if you are looking for a 4Man trash setup or if your group isn't providing all of those, you need to adapt it (Adding Crit CPs, use OW, more Light pieces, etc..).
The main trash set is Sul-Xan, you want it everywhere, but the 2nd set is flexible, you can do OW, Briartheart, Burning Spell-Weave, Scathing Mage, Heem-jaas, etc..
Maelstrom Bow backbar is better than the staff, if you can sustain it.
If you plan on using Bow/Bow setup in the rest of the trial, don't use Barrage but Volley.
Mage's Wrath isn't bad but in general Spin will hit harder, and you generally want to keep your mag to streak.
You can use Dark Deal to prebuff Prophecy for your group, but you can also rely on a frag cast at the end of the last trash pack.