I’ve appealed several times and got my assessments lowered before the hearing occurs. They will call you well in advance of the hearing (which must happen within 2 years of your filing the appeal) and try to reach a compromise.
Right now over 40,000 appeals have been made in San Diego County. I’ve attended the hearings, where numerous well-paid county employees attend and only resolve about three cases per hour. If you do the math, less than 1% of appeals go to the hearing stage. That means they really, really want to come to an agreement with you. So hang tough and they will budge.