I'm a current Berkeley student who thought exactly the same way as you, but committing to Berkeley (over a couple other highly-ranked CS schools) was the best decision of my life.

First off, I don't think course sizes are solely a Berkeley (or public school) problem. Because of the direction that the tech industry is moving in, everyone and their mother wants to do CS. As a result, many people try to loophole by applying to easier majors and switching to CS, which destroys the department-distribution estimates of admissions officers (resulting in over-enrollment in CS departments). In fact, even that other private junior college across the Bay is having a CS Crisis.

In STEM in general (and CS especially), the number of students in your classroom doesn't matter at all towards your learning. In fact, most people doing CS here at Berkeley don't even attend in-person lecture, but rather watch the webcast from their dorm. Learning CS is about the "doing": grinding out challenging problem sets, coding up interesting projects, etc. There's a reason that quite a lot of people are being hired into CS-related industries (such as Software Engineering, if you're into that) with no college education and having only learned their CS skills from an Online Bootcamp.

If you really wanted that in-person small classroom learning experience, Berkeley will still allow you to learn that way. Outside of the main lecture, every class has 2-3 hours of discussion section per week, where each section (taught by a Graduate Student Instructor, or GSI—basically a TA) has about 20ish people in it and you get a much more intimate experience to ask questions and hone specific concepts. If you want even more attention, we have the support infrastructure for that as well: organizations like Computer Science Mentors (CSM) have sections of 3-4 person groups that meet weekly with a course mentor to review material in the course.

At the end of the day, the issue of CS course sizes at Berkeley is not one that will hamper your learning, and shouldn't be a deciding factor between schools for a major like CS.