I have lost one battle since the first day the falcon came out (the event started after my payout so didn't swap until the next day) and it has very little to do with RNG. Its all about what fleet you use and how you use it. Cassian's U-wing dispelling buffs is the key, followed up by the special that calls an assist. I have the Falcon at 6 star and can take out a maxed 7 star falcon with this move. As long as you don't have breach on one of your ships it has worked every time. In fact the only battle I lost was because I didn't see the breach on my HT and had to target their HT instead of their Falcon.
Its no different to Arena in the fact you have to work on your roster to be successful. The only difference is that it involves characters that people consider 2nd rate or lower, so please continue to hold this approach and I will collect first place, 1800 fleet credits and 20 zeta mats every 21 days without having to worry about the RNG from the 3 challenges each week, not to mention the 400 crystals