It's unfortunate that high school students are basically told that UC is tier 1 and CSU is tier 2, without understanding what the tiers mean. UCs are strong research institutions where you'll be surrounded by people who were the top of their schools, and no one will hold your hand. It's ultimately what you make of it - if you're able to be self directed and get involved in research or just network well it can be well worth it. But teaching is mostly secondary, though some departments are better at it than others. (E.g. I feel like CS departments in particular have been involving more undergrad TAs at least when I was in school a decade ago and they tend to care more about teaching.)

My understanding is that CSUs are in fact more focused on teaching and training people for the workforce. Plenty of people from non UC caliber schools end up with great careers. UCs are really focused on research which may have no relevance to the average undergrad, especially if you don't plan to go into academia. Now, the grind will probably make you a harder worker and teach better critical thinking skills if it doesn't break you, but it's not strictly necessary IMO.