This is not that plausible as an analysis of the role of chargemasters.
I agree that the chargemaster prices are fake, but what you are proposing is:
Hospital: "Our insurance partners pay us a fraction x of Chargemaster charge X, so let's make C larger."
The insurer understands the game being played here, just like you do. It's not like the insurer doesn't also realize just like you do that the chargemaster price is fake.
The insurers are not going to say "Oh C got bigger this year? Well, let's pay more!"
More important are failures of competition in the marketplace, especially consolidation on the hospital side (most markets are now served by large hospital systems, so insurers cannot plausibly threaten to exclude hospitals from networks), the lack of exposure of consumers to most of the price, and the lack of incentives on the consumer side to search for cheaper prices (plus a general lack of any information about which facilities might be cheaper).