I just did it with:
Tarkin (L) 6* L76 g8, abilities L7 (omega basic)
Vader 6* L80 g9, abilities maxed (no zeta)
EP 6* L80 g8, abilities L7 and omega on power of the dark side
TFP 5* L73 g8, abilities L7
Snow 4* L60 g7, basic L4, AOE L6 and unique L7
I tried many times with RG in place of snow, tried EP lead, couldn't get past stage 4 of tier 1. Then I decided to level up snow as best I could, and beat tier 1 on the first try. His unique is crucial. Also I had lots of speed on EP (69 from mods) since i rely on his stun so much and needed someone to go before the ewoks in stage 1.
With the credits I got, I leveled up Snow to 70 and barely beat tier 2 after about 10 tries. Can't do tier 3 because he's not 5* (and can't get him there today).
I'm FTP and started playing 4 months ago. Luckily I worked on my empire guys for the R2 event, and more leading up to this one since I saw what was required. I agree the event is frustrating and if you don't have snow, you probably need toons well in excess of L75, g8.