Yesterday I fought a few times against Chaze.
My Biggs goes first and removes Baze's protection. My Boba is next but if I execute now, I lose.
So the key was for me to safe the execute and hit my ability block. Then come my AOE (Lando, Wedge).
Next round, Baze had so many buffs that my execute kills him (35k dmg!)
One time even the second round of Biggs killed Baze already, so I executed Chirrut.
I also lost one fight because that execute missed. That problem will only be solved with the omega (lvl 84).
So fighting Chaze is all about timing and landing your execute.