My Rebel team strolled through to Round 8 on Military Might I. It then took me four attempts to beat Round 8 but I finally did so, unlocking Tier II in the process. I still get to Round 8 with rel...
I have had good luck with Zody lead clones or Princess Zody squad. The Clone team uses Rex to resist the stuns and it's pretty much game over. Don't give up RNGesus will help eventually.