I think you are referring to the maximum increase in tax basis value (which is only equal to the maximum property tax increase if it is taxed at the maximum value already, though that's probably the case, given the low cap on property tax rates also in Prop 13.)
And you are oversimplifying in a way which is misleading in this discussion: new construction triggers full cash value assessment not limited to the annual 2% increase.
> AIUI, SF could waive any property tax increases for residential properties that would have been triggered by flattening the existing structures in order to build much more rental housing.
To the extent that they could, where would the sense be in that? Accommodating more people, but reducing the public available to provide services needed by those people?