Imo, this is what needs to be worked on:
allowing healers to heal protection.
Either doubling the awards or minimizing the time needed to complete GW.
Doubling the time for arena battles to 10 minutes.
Minimizing the dodge rate. Dodge is suppose to be 15% and I've seen dodge rates as high as 50% and the chances of that happening is less 5% of the time-and I see it happening most times I battle dooku/lumi teams. Even without them as leaders, the dodge rate seems high still.
And personally, maybe fixing Old Ben and Mace windu? Both are pretty weak and I paid to get windu and ben is tedious to get. Some fixes would be to add a shatterpoint that does more damage for mace and then add a fourth move for Ben- people like the taunt, for instance.
Also, I think challenges are fine. I run them with a few 7* and a few 4/5* and I seem to be ok. It's harder and I'm not on the tank challenge and that tends to be the hardest, no doubt. But, making them any easier and you'll have to change the name from "Challenges" to "Give Aways"