Droids are still viable (moreso now with Chopper being added imo).
The traditional droid team of Hk (L), 88, 86, JE, and B2 (or Nebit in certain situations) is still plenty viable in arena. They can beat nearly anyone on offense, with a few exceptions.
Here's the issue: They lose nearly 100% of the time on defense.
I have the above people maxxed out completely with decent (not game-breaking or kraken-like) mods on them. I was placing top 10 daily on a pretty competitive shard. The issue was that I had to use a refresh to do this - as I found myself placing anywhere in the top 10 (depending on how certain teams were positioned) and then falling very far - sometimes out of the top 50 - overnight. So then it's a haul to get back up to the top again. It's exhausting - even if you come out on top with the crystals. I had one day where I managed to snipe the top spot in arena - then fell back to 48 overnight.
So it's discouraging. If you run droids - you have a giant red flag on your back that says "Attack me! I'm a droid user and an easy win for you!" - and everyone knows that.
I switched to Zaul and have had 0 complaints since.
I love droids and they are viable - they're just a huge heachache. My thoughts are Chopper may change that. JE uses calibrate at the beginning of the battle, and chopper does his dispel on the opposing team's auto-taunter. For Baze teams - Chopper would kill the taunt and also reduce 20% TM for everyone (taunt and retribution). That means you will get (roughly) two full turns with your droids before the opposing team even moves (possibly more with good assists on 86 and if HK lands slow on his AOE). Again, it doesn't give you an "auto win" against the teams that are difficult for droids to beat (Rex leads, Zaul, etc) - but it makes droids a heck of a lot more viable.