There is such a thing as employee and corporate bargaining power. Many SV companies adopt gold plated health insurance policies on top of competitive wages. I suspect hat this extra bit of health insurance helps prevent the perception the employer is overbidding on labor.

Similarly large corporations can negotiate to get better insurance rates, and larger insurance providers negotiate to get more cost effective care.

(One of) the problems with the health system in the US is that once you exit this negotiation scheme, prices go insane. A hospital might list a procedure for 2 million dollars only to take home 50k from the insurance provider. I don't believe anyone has a handle on what the true cost of any health procedure is.