Use your best 5 toons until synergies get better. On the other hand - in PvP you do not even need a healer. Lumi as an attacker heals enough in your PvP squad. Try to get some hard hitters/assist caller and take out Talia and JC. A lot of heal = attackers will outrun you = you are a primary target in Arena. Keep Phasma Sid and Lumi for a while. You might concentrate on Ahsoka (hard nodes/Cantina tokens). And i would recommend farming Geo in Cantina.