>Cuban is saying they don't even do that - they don't track their costs on a surgery by surgey basis at all. And because they don't track any of that it's impossible to reason about it.

Then Cuban is wrong. I had a heart valve replacement surgery last year and I got a detailed to the penny to the mg of tylenol what they consumed and what they charged. It was not a big massive one line "heart surgery" on the invoice, there were dozens and dozens of line items. I think quite the contrary they know exactly what their inputs are to a surgery, it's just that is not the only cost you get billed.

>because you don't have any of the data on what the costs will be when person X needs a given surgery

This was exactly my point, and yes part of it is because of cross-subsidization, but it is also because my valve replacement almost certainly cost someone differently than the next guy having the same surgery the next day because of any number of factors

Also part of determining insurance costs is that you probably don't know which surgeries someone is going to need at the time the premiums are being set. Even if you knew perfectly how much every surgery in the system costs, you don't know how many of those surgeries you are going to have to pay for