Well I finished 7* IGD shards today and I went into the last Yoda teir with a lot of confidence. Man was the rug pulled out quick. With IGD as lead I managed to get the little green troll into the red once or twice but then he would rampage. After about 20 tries I decided to try Lumi as lead. Things went better for a while. Then I would switch back and forth. I think around the 50 try the RNG Gods shined on me. I had Lumi lead with JC, QGJ, IGD, and EK. Came down to Yoda and Bariss in red and my QGJ and IGD in yellow. Went for the assist on Yoda he dodged both and I thought I was about to lose. The I got 3 dodges in a row, 1 on QGJ and 2 on IGD. I finished off the green goblin and sighed in relief. It's over victory is mine.
TL;DR
I thought IGD would be the best leader due to his leadership ability. However you don't get as many counters as you would expect. It's supposed to be 35% but I went entire matches with multiple Yoda aoes not triggering even 1 of the 5 to counter. Lumi is the way to go and a lot of luck of course.