Owens valley, where LA "steals" water from, is on the eastern side of the Sierras.
NorCal, including Sacramento, is on the western side of the Sierras.
So unless they planned on pumping the water over/under the mountain range that surrounds it in every direction except for towards LA, that water was never available for any NorCal city to use.
Owens valley is basically dried up from the water that LA takes. It's interesting as you drive in the towns in the Valley and you see all the LA Department of Water and Power offices over 200 miles from Los Angeles. The courts had to force the LA DWP to quit taking too much water from the streams that feed Mono Lake as it was in danger of drying out.
LA also gets water from the state water project which does come from northern california: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Ca...
they are saying that LA takes water from sources which would otherwise drain into the sacramento and san joaquin river delta. The video from this post mentions the California State Water Project which takes water from the Feather River (Oroville Dam) and distributes it along the Western edge of the central valley South to Bakersfield where it is then pumped over the mountains both towards Los Angeles and further East to San Bernardino and Riverside. It provides way more water to SoCal than the two Los Angeles-specific aqueducts from the Owens Valley on the Eastern side of the Sierras.
Old men yelling at the sky don't often seek rationality or nuance in their cries.
The California Aqueduct delivers water from the western Sierras through the Central Valley and to Los Angeles. This is likely what NorCal refers to when they say SoCal is 'stealing our water'.
https://en.wikipedia.org/wiki/California_Aqueduct
Would be interesting to see the relative amounts of use by LA and by agriculture in the Central Valley though.