I think your statement sounds perfectly reasonable, but it actually holds a pretty interesting corollary! If he is wrong that "most" medical treatments and prescriptions are worthless then that would necessarily mean that "most" are valuable. The reason this is interesting is because the exponentially increasing rate of both the amount of medication out there and the amount people are using. For instance from 1997 to 2016 the number of prescriptions filled grew from 2.4 billion to 4.5 billion [1]. And an exponentially increasing number of people, across all ages and demographics, are also being medicated with all sorts of drugs for various reasons.
So, if we assume that most medical treatments and prescriptions are not worthless we should see increases in healthfulness that are at least somewhat comparable with our increases in pharmaceutical usage. In reality we saw sharply diminishing returns on life expectancy that have now gradually shifted towards an ongoing decline in life expectancy over the past few years. By any standard of effectiveness, this is not looking good for pharmaceuticals.
So I suppose I'd turn it around. I think the view that medicines (and especially their recent exponential growth) are providing a substantial social benefit could be true, but it would seem to be the statement that needs to be explained. E.g. perhaps our own increasingly unhealthy lifestyles are contravening the gains from the medical technology? No idea there, but I do think occam's razor would tend to simply suggest that the reason we're not seeing improvements is because we're not improving.
[1] - https://www.webmd.com/drug-medication/news/20170803/american...