It’s a fair point in some regard. However, you could show that diversity in the universe via the Rebel fleet pilots. That would give more weight to the Rebel Alliance to show how this isn’t just a human fight for freedom, but every alien’s fight too.
Chewie would have something more to do as well in the story. Perhaps it doesn’t have to be a Wookiee planet, but a place where many Wookiee slaves are imprisoned there by the Empire, so with Chewie’s help, frees them and overruns the Imperials there. Introducing Ewoks in one and only movie has that issue of trying to tell their own story, their culture, etc when there’s so much already going on and slows down the movie too.