I think arriving at a hard percentage would be difficult, but I don't see how it is controversial that US government funded research has been well supported by capitalism and contributed much medical knowledge, or that there has been lots of private research and development work in the medical field in the United States (I guess lots and lots of development has been privately funded).

Of course, that history played out that way is a different argument than claiming that we could only arrive at our current level of medical knowledge by that path.

All we'd need to do is look at the tax code for health care businesses.