What makes a particular property owner into a ‘squatter’?
Prop 13 is a blunt instrument that rewards speculators more than it protects homeowners. What would be a much better system is some sort of forbearance, that the owner does not have to pay the full property tax until the property is sold, and then the back taxes are paid from the profits.
Immortal entities like corporations should not have Prop 13 protection.
Unless you take seriously the idea that most homeowners in California are squatters and NIMBYs.