I will also comment that when we talk about "healthcare being a market", we need to separate out providers of healthcare, with insurers of healthcare. Insurers of healthcare are much closer to a market (in that I can generally find out what the cost of the insurance is, and what it covers), but providers aren't (in that prices lists are hidden, it's not clear what is covered vs what isn't, etc). We talk about the cost of the insurance, but that's artificially high because of the practices of the providers (themselves incentivized to behave that way because of the insurers).

And that's the open market; it gets even more cloudy when we talk about employers being involved, so we have an agency problem as well.

It's a system unlike any other, and I don't think general theories really apply very well as such.