The draft Economic Sustainability Plan for the Delta places the total size of Delta agriculture at over 423,000 acres (excluding grazing land). With land retirement, Westlands effectively only has 468,000 acres, and it is looking like they will have to take more out of production in the coming years.
So the Delta is really of comparable size to Westlands. Westlands has also been shifting to a lot more wheat and pasture crops, so the total value of crops grown should be more comparable.
And the Delta has water already, of adequate quality if it is managed for Delta agriculture and fisheries rather than for export.