I will not argue with you about this. To the contrary, I think you are right on the facts. However, some folks I know who went to UCs highly value the lessons and skills they feel they learned from the scrappiness and self advocacy required to get the best from those schools. They feel very strongly that those skills would not have developed to the same extent at a school that does more hand holding. I am very familiar with the UCs, and I do not think they are wrong about that. And, if one has that kind of moxie, the rewards one can get from the opportunities available and the professors and students and industry around are top notch. So, that is the case for the worth it I alluded to.
That said, if comparing to Brown. You will get all of the top notch place benefits without the need for that moxie at Brown.
And, to be clear, while I think it is worth it to me, it is totally reasonable to think it absolutely is not. And, for anybody who has seen my posts here, they know that D26 is only applying to small liberal arts schools at least in part for the reasons you identify. I am also of the view that smaller schools actually do undergraduate education best. The institutions prioritize and reward faculty for undergraduate teaching and mentoring. Large R1 research institutions prioritize faculty research and graduate student education. Undergrad education is often second fiddle. The UCs would fall into this category. But for the right kid, I still think it would be worth the money.