I ran Jyn (lead), cassian, K2, chirrut and baze for about 4/5 months in arena and slowly zeta'd them in this order:
Jyn lead
Cassian
K2
Jyn unique
I was able to get 1st every day in arena (once they got to G11) except if a GK/ Barris team was still in 1st but with all the CLS coming in it was dropping to far on defence as yes, the DPS comes from Cassian racking up the exposes and K2 taking all the damage - although CLS started putting buff immunity on him so became worthless.
Now I run CLS, Jyn, R2, Chirrut and Baze which I think is a shame as I preferred running the R1 team, the AI just didn't seem to work the expose as well as it could have.
Jyn's unique is actually very useful now as she is immune to CLS', Han's and R2's stun so you don't have to worry about the counters so much. Is fun when Han's shoots first goes for Jyn.