Improving my formation, advice needed

DarthVanio

So after a week of struggling, I finally am back at top 10 at my Arena server. The problem is that I am F2P and my team is running out of time. So I need some advice bout how can i improve and get my team to the higher lvl. I got :
Sid - 6 (almost 7*)- full gear
Lumi - 7* - full gear
JC - 6* - full gear
DM - 4* - full gear
Ima gun - di - 4* - full gear

My other characters which i keep farm and play with are :
Boba 4* (almost 5) - full gear
Darth Vader - 4* - full gear
Phasma - almost 4* - V gear
Talia 5* - full gear
Asajj 3* - almost full gear.
I have no problems with GW but in the arena is getting harder and harder with all of the QGJ and Bens. I was thinking of taking out Gun - gi and DM and bring Vader and Boba in for now. I know that with this form my burst will go down, but i thing this form will be more viable - with the skill block and the one shot potential of Vader + Sid combo. I am working on Phasma and Boba, and after i finish Sid i will go for han/eath. I need some advice guys, it will be great.