The RNG is not the real problem. Random swings will happen.
The real problems are characters that can one-shot other characters of comparable power easily, and the fact that this is a turn-based game where teams can manipulate things so that they get 4, 5, 6 or more turns before the other side can do a thing: https://forums.galaxy-of-heroes.starwars.ea.com/discussion/5254/the-real-problems-with-the-current-meta-too-many-consecutive-attacks-and-too-much-damage
A fair turn-based game cannot be designed so that either side gets the majority of the early moves, no matter what the synergy of the team. The Poe/Phasma teams are broken.