JC is quite bad for arena, buta powerhouse of fleet arena so still worth leveling up.
My point was that, following OP guidelines, I got stuck being forced to use JC in arena. Otherwise I get nuked before I can take any action. Still manage to get top10, but it's as you say - I get sniped easily and have to work diligently before reset to get my spot back. It's getting harder and harder. I have no idea how OP was able to get any decent top spot with his arena team, he wouldn't be able to get in my top50 with it. Would get blown up before phasma could do anything useful.
When it comes to Baze it's hard. For me it's a coin flip here, since I have to go with phasma, qgj, gs, sth and jc. It's a nighmare matchup. Basically 2 strategies: cleanse his buffs with qgj and try to burst him (works 50/50 for me but only if I got assisted attacks from gs, qgj and phasma proc) while sth taunt is up to boost your TM. Second - tricky, but doable - strategy is getting him to retaliate onto sth while retribution is on him, so your units can attack him twice, before heal over time kicks in. It's only doable after turn 2, so he wont dispell taunt.
Sun Fac is the way to go, from what I heard. Also read about empire team doing quite well against him, with vader zeta (omega?) - it reaplies debuffs after they get cleans, so chirrut isn't helping that much there.