https://covid19.sccgov.org/dashboard-case-rates-vaccination-...
The number --- 871 cases per day per 100,000 unvax'd, for the week preceding 1/10-- is an amazing rate (7 day average). It tells us that 6.1% of the unvaxxed population became a case during a 1 week period. This doesn't count people who were infected and did not test or did not test in a way that got reported.
Your point about whether mild infections are slipping through is interesting. Probably the vaccinated have more paucisymptomatic infections. The unvaccinated and vaccinated probably test at different rates (which way? required workplace testing of unvaxxed vs. unvaxxed more likely to be deniers who don't want to test). Etc. So there's some confounds here, for sure. But boy that 871 per 100k number is fascinating.
Without reinfection (which we don't suspect is likely for Omicron-following-Omicron), it certainly can't stay at 6% of the population per week for long. I doubt they have spotted more than a third of infections.