The two biggest classes I took in college were with “famous” professors who in addition to their academic reputations, routinely won prizes for teaching and mentoring undergrads.
I can’t imagine opting out of these huge lectures-- which were incredible and life-altering and inspirational- to take a 15 person class with a hohum professor.
Sometimes the reason classes are big is because upperclassmen tell entering students “whatever you do, do not miss out on professor A’s class, even if you have to sit on the floor and even if they cap enrollment”.
So average class size is important except when it’s not. In my major- Classics- every class was small (and some were tiny). Bio- classes were bigger. Egyptology- the ratio was usually 1:1. Psychology- bigger for the first two years and then small.
These “averages” mix apples and oranges so you need to understand what you are looking at when you evaluate how important small classes are. You can never have a large lecture, depending on your major, or you may not have a small class until senior year when you’re in seminars and 1:1 teaching for your thesis.