Yeah. You seem to be right in that in-between stage. Your arena squad is shaping up to be great down the road though. Maul is one of my fav characters from Clone Wars.
I'd recommend trying to stick some Potency on Maul and see if that doesn't help your chances against JTR and CLS squads (with his daze attack). JTR is always going to be a little tougher because they don't carry as many rebels so Vader isn't getting that extra speed.
You could always experiment a little with getting CLS geared up and sticking him in there. Also, your Hera is pretty strong (I'm jealous) and this is a bit unorthodox, but maybe see if you can get her to do an assist attack and then drop "backup plan" on Sion or DN. My guess is you're having issues with their survivability during battles.
I hope we're not overwhelming you, it's just Maul is not good outside of the leader position. But on the plus side you have him G12 so his ship is going to wreak havoc in ship arena for you.