I've always thought that the rebellion was to united and nice.
A rebel movement in something as large as a galaxy should have a ton of competing groups in it, united only by their hatred of the Empire. Some honorable and some little more than terrorists.
The name of the rebellion says it all, The Alliance to Restore the Republic. But there are plenty of groups that while opposed to Palpatine also have no desire to bring back the Republic.
Though I seriously doubt I'll ever have time to write it, I've had the idea of a story where a darksider character launches their own rebellion against the Empire to try to create an independent darkside aligned state in his area of space.
The character would spend almost as much time fighting with the other rebels as with the Empire, and even at the best of times have very frosty relations with them and especially any Jedi working with them.
The point of the story would be show messy and diverse a galaxy wide rebellion would be. There should be groups that want a unified galactic state, others who want their own independent states, all sorts of different darksiders and lightsiders of different stripes, alien supremacists, human supremacists, republicans, autocrats and so on.