I guess it depends on what part of California you're talking about but all-seasons will generally outperform equivalent grade summer tires in the rain if temperatures start falling below 50-55° or so. A summer tire's grip falls off precipitously [1] when temperatures reach 40-45° but the loss of grip in that "NorCal winter" kind of weather can reduce their performance below that of all seasons. Just because they haven't lost a dangerous amount of grip doesn't mean they haven't fallen behind the grip available to a tire with a more temperature insensitive compound.

[1]: https://m.tirerack.com/tires/tiretech/techpage.jsp?techid=27...