Reliably beating Jedi Training Rey with droids and Kenobis

The other half of this is that a good CLS or RJT team can shred a NS team. In the current state it seems that GK/zBariss might be the odd team out.

Your idea with an Empire team has promise too. You might want to look into that a bit. I'm not incredibly familiar with DS/Empire in arena but I do know there are a few comps that can do quite well. Thrawn, ShT, DT, Krennic, Veers, Tarkin all seem to be viable options.