“If you’re in the 80th percentile for grades and test scores, were your essays so deficient that you should get denied across the board to the upper half of UC schools?”
Since the UCs are for the top 9% of Californian students, and the “upper half” are therefore for the top 5% or better (typically top 3% for UCB/UCLA: ~15K admitted out of nearly 500K CA high schoolers when allowing for those who get into both), it stands to reason that students in the 80th percentile aren’t going to get in except from the very best high schools in the state. The essays don’t even matter at that point. There are plenty of CA high schools where hardly anyone gets into UCB/UCLA, especially amongst those schools with a high proportion of disadvantaged students.
The reality is that compared to the top private schools, UCLA and UCB give out proportionately fewer spots to those with hooks (e.g. sports), don’t consider legacy/donations and aren’t allowed by law to consider race. And they look at all applicants from a single CA high school side-by-side when deciding who should be admitted. So it’s actually rather more predictable that the top few kids in the class will get in than for similarly selective private schools. That’s a lot less like a “lottery” than USC or Stanford (unless you buy your way in there).