You are more right than you know. Benefit mandates on health plans are a major reason for their high cost. At this moment, the house passed a bill to make mental benefits the same as all other benefits.
It will add about 10% to the cost of most plans.
Adding mental benefits will, over time balloon costs out of control because the science of mental illness is entire subjective. If the patient claims they feel a certain way, well it must be covered.