It's really easy to verify that this claim is pure nonsense - we still have very real, astonishing scientific progress.
And then, put the number of contributors and the rate of progress against one another, my guess is that you would see a massive slowdown of progress, so massive actually, that explenations about the slowdown abound. There is the "all easy apples have been picked" theory, the "only life&death systemic competition forces contributors to produce good science" theory and a ton of others. All basically trying to explain the same phenomena- which could also be explained by: "hackers, hacking hackers, hacking processes, leave no financial substance behind to have people who actually do the scientific leg-work."