Some institutions lean on their work study/Graduate student/TA population to teach lower division classes, assist in grading , or leading tutoring programs. I think that the the Carnegie rating of an institution may play a factor into the frequency of which GAs are used. The higher the R1 or 2 rating the more research intensive the school is.
My husband and I both attended an R1 institution and were GAs while in graduate school. I worked in the civic engagement office, he as an instructor. We were capped at 20 hours/week. While the pay was ok at the time, the important part was the free tuition that were were provided. The downside was that your load could be very heavy as a GA. My husband loves teaching and his class sizes varied from small 30 student lecture classrooms to the 500 student auditorium for a 101 level course. He didn't teach just one class but might be teaching two or three, and depending on the class size did his own grading. Department budget could also impact whether you had additional TAs to assist with grading.
I don't think that the GAs striking is out of line. Free tuition is great, but you still need to pay for a place to live. If the amount that you're provided in your aid package is not covering your basic living expenses, then there is a problem. On-campus housing is limited. I do not know what the availability or pricing is in Berkeley, but know that it can't be cheap. Rental pricing has been increasing in the last few years, making on-campus housing more competitive to get into, as in some markets the prices are locked in to when you started at the university.
Another thing to keep in mind is that as a GA/work study student that you need to maintain eligibility for your position. Not just academically, but financially in that you do not make more than x amount. Making above a certain threshold can make a student ineligible for their GA/work study position or reduce their aid award package.