Classical economics holds that if law firms charge more than what in-house lawyers are willing to pay, those fees will decline. If demand is less than supply, prices fall.
Absent a monopoly, and no law firm in the United States has a monopoly on any legal service, and absent proprietary knowledge or processes, and no law firm has a patent on any legal service, supply (cost of law firm services) should reach equilibrium with demand (legal services valued enough to be paid for by companies).
If this axiomatic economic reasoning applies, then the grumbling about the high costs of law firms and a systemic gap between what is paid and what is gotten is sound and fury signifying nothing. Demand matches supply, ergo no value gap exists. QED