The reservoirs are designed and calibrated for specific times and rates of fill, largely driven by snowmelt runoff rather than precipitation deluges.
Aquifer fill rates are slow, and are generally predicated on large-scale flooding. Prior to modern flood control (dams, river channelisation, levee construction), in which much, and occasionally effectively all of California's Central Valley (as well as large riparian valley systems in Oregon and Washington) would flood.
See the Great Flood of 1862: <https://en.wikipedia.org/wiki/Great_Flood_of_1862>.
Reservoirs provide parlous slim protection against landslides of elevated slopes. Those are affected by upslope water saturation (the stuff that's on its way to fill your aquifers in coming months or years), not floodplain innundation. It's exacerbated by fire-cleared hillsides, particularly those which burn ferociously hot, killing plant roots and baking soil. Those fires are not historically typical, but have been the conditions experienced with greatly increased frequency since the 1990s.
Cattle don't graze chaparral, oak woodlands, or ponderosa or Douglas fir forests. Those have been what's been burning.
Your suggestions / assessments are at a far remove from reality.