When I think about class balance I fall back to SW and the Jedi. Pretty much most players want to be a Jedi because they are (or were at least) a large focus of the media/stories. Also, with their Force powers they are more powerful in many ways.
Now, it has been decades since I played WEG d6 SW, so honestly I don't remember much about it as far as balance goes, but I do remember about d20 SW and in many ways it was more balanced in power because the Force abilities of Jedi were not nearly as powerful as magic can be in D&D. So, IME balance was easier in d20 SW than it is in D&D when it comes to comparing difference classes. Of course, different classes had features which more emphasize different foci/ niches in d20 SW.