Teir 4 - Special Op 3 strategy?

I finally got it done, but in the end I think it was pretty much RNG. Phasma lead, FotP, Kylo, Boba, and Daka. I was finding stage 1 to be quite frustrating, so I unloaded on it to burn them down. I started stage 2 with Phasma and hit march - every other time those rebel scum get in a good 5 attacks before I get my first turn. Execute on Baze, one shot of Chirrut (thank you FotP!), stun of Cassian, then mopping. All told took me maybe 20 times.