I wouldn't say Im a rebel master but in my experience I've found the rebels to be much less forgiving than the Imps.
Yes they do have ship synergy but that makes it much harder to get everything to work together to their maximum potential. As a result I think a reb fleet played well can be incredibly powerful. But if the reb player makes a mistake then *POOF*, they've lost a ship and they can say goodbye to some of that synergy and it makes it much harder to win the game.
In my experience (again as a padawan) many of my wins have come from an Imp mistake that I've been able to exploit rather than my reb lists being stronger.