Rtrooper does the majority of the damage on that squad. His special CD resets when he attacks a target with Expose.
I have been getting better results from using Holdo than RScav, cause the heals and passives keep my team alive longer, but RScavanger does work if your very careful. There are some very good videos of how to use resistance squads in the STR, after watching a few I am able to get BB8 to use his Illuminated Destiny before DN gets his first turn. My guild is only doing 5 star STR but this team posts 5.5 mil or more damage routinely.
When farming and such permits, I plan to set up a second Resistance Raid team with Finn leading.