The key point is that the difference between "wholesale electricity" and "retail electricity" is based on total costs which don't change if you buy 1kWh less fr

The key point is that the difference between "wholesale electricity" and "retail electricity" is based on total costs which don't change if you buy 1kWh less from the grid - while it's currently priced "per kWh", it's not really a marginal cost but a fixed one, so people in aggregated would have to pay the same total amount to the grid no matter how much home solar panels are built. There is a cost advantage currently, but that is a side-effect of how we currently do accounting of grid costs, not reflecting any actual advantage in reducing total costs across the country.