Over the course of its four seasons, Star Wars Rebels subtly rewrote so many parts of the Skywalker saga. There’s a sense in which Star Wars Rebels can be seen as Episode III.5 of the Skywalker Saga, because it takes place during the Dark Times of the Empire’s reign. It’s a little different, though, because the heroes of Rebels are one step removed from the main story. This made for a far more exciting show, because anything could happen; their fates weren’t sealed by the movies, meaning their survival wasn’t guaranteed.
https://screenrant.com/star-wars-rebels-skywalker-saga-changes/