Equity is not the only concern, though Prop 13 is certainly a transfer of wealth too established, richer people from poorer, less-established ones.

Prop 13 also incentivizes people _not to move_. This adds friction to an already high-friction market: people are disincentivized to upsize/downsize, move closer to work, etc., which harms the market beyond just the fact that it's an inequitable wealth transfer.