I use Ewoks and have opened up a T5 raid against the pigs with a 750K damage single attack run. All because of Teebo lead and turn meter manip. I use Teebo, CC, EE, Phasma and Foo. I would certainly replace Phas and Foo with QGJ and 5s if I had them but don't so...I use them.
The key is to get started properly. If the battle doesn't start perfectly, retreat and try again. And by perfectly I mean, Phasma inflicts speed down, Teebo self-stealths AND his first hit drops the TM on Rancor. Then I strategically use Phasma Victory March only in those crunch times when Teebo didn't stealth and I am still in cooldown. So I'll use VM to give him another chance to self stealth and even FOO for pinning shot to reduce TM and other strategies. Don't lose faith and give it a few more tries. When you get the groove going, you will love it.
And yes Rancor is immune to TM reduction when toppled. It says that in the description over his head when you drop the door.