The mutual insurance companies that insure many doctors are owned by the policyholders themselves. In any event it proves nothing that liability insurers prosper when liability expands. Litigation is what sells their product. Profit comes from assessing the risk and then covering it. Big risks require more insurance.
Nobody has any reliable numbers.
The reliable, bottom-line measure of how much the liability system costs is what people pay to insure against it. These are hard numbers. For several decades total expenditures on virtually every class of liability insurance have risen much faster than inflation. The federal government, states and municipalities insure themselves, and they know they've been paying more. The figures get soft only when you try to assess the additional, indirect cost of laying paper trails, engaging in defensive medicine and not building small planes.