Imo chaze under cls lead is not much difference. Bcause basically they already have their own build in counter attack ability. Been testing cls under wedge too, with cls 260 speed he seems slow. I think cls will optimal (still) under rex lead.
With rex any combination is work:
Rex - cls - thrawn - R2 - gk
Rex - cls - thrawn - nihilus - gk
Rex - cls - thrawn/nihilus - chaze
I think with the appearing of cls not bring much change in arena.