The CA law makes a screwdriver a dagger since is "instrument...capable of ready use as a stabbing weapon". But then more people are stabbed with screwdrivers than Cold Steel knives
Not necessarily. There is a lot of case law in California regarding under what circumstances an ordinary object with legitimate use can be defined as a weapon. Like for example- if the item is modified so as to make it a more effective weapon (like sharpening the tip of a screwdriver to a fine point).
Also, in order to obtain a sustainable conviction for carrying a concealed dirk or dagger, among other things, the prosecutor has to prove that either the individual was carrying the item as a weapon, or that they knew it
could be used as a weapon. Which is often made easier by individuals who admit to the cops that they were carrying the item "for self-defense", or who simply acknowledge to the officer that they knew it could be used as a weapon (Cop: "You know that can be used as a weapon right?", Person: "Yes". That "yes" can be used by a prosecutor as an admission of guilt that the officer will testify to in court).
There are provisions in California law (People v Aubrey, People v Oskins) that specifically protect people who are caught carrying items that can be used as stabbing weapons, but who were doing so innocently, including the concealed carry of fixed-blade knives. To use the screwdriver as an example, if the cops stopped someone for some reason and found a regular, un-sharpened screwdriver concealed on their person, as long as the person did not admit to carrying it as any kind of weapon, and as long as they didn't acknowledge that they knew it could be used as a weapon, then they would not be guilty of a crime because a screwdriver is a legal item with lawful uses.
One relevant case law on this matter is People v Rubacalva. And a few case laws that are referenced in People v Rubalcalva are People v Forrest, People v Barrio, People v Grubbs, People v Aubrey, and People v Oskins.