Hope this helps you...
last time i got r2d2 at 6 stars with Tarkin, vader, magmatrooper, royal guard and couldn't beat tier 7 with bad mods
tarkin G11 135speed
vader g11 134 speed
tie advanced G9 186 speed
magma trooper ans stormtrooper just G9 no mods
i did it with just tarkin vader and tie advanced the others died fast
+30 speed arrow on vader and tie
it was very important to put protection on vader
tried to follow croungchinrancor mod adviser on vader and tie.... not perfectly
potency mods on tarkin..
and some speed secondary mods(from my arena team)
Tarkin lead, gives more speed
first aply debuffs with vader and tarkin increasing tie pilot basic
did ultimate fire power after 3 or 4 turns(TARKIN increases potency)
culling blade killed instantly luke and leia...
i killed first r2d2 than chewbaka and old ben
thats all this event is just about getting the right mods and i think this could be done with lower gear...