They show R&D is effective and R&D spending is up, and conclude obsolescence must be the reason this is not reflected in productivity pretty much by process of elimination. However there is an alternative - that for reasons unrelated to R&D, productivity is actually being driven down, and ever increasing R&D output is necessary just to maintain current levels of productivity.

In particular, they are looking at US manufacturing. While this is a diverse industry, it's clear that in many subfields there is quite a bit of saturation. When everyone has a car, and cars last longer and longer, the need for new cars goes down. Once you get to a point where your industrial capacity can provide enough to satisfy demand, further R&D only reduces the costs of satisfying that demand, not increased output, and in some cases improvements to product quality may even further reduce demand. In the US, light vehicle sales peaked in 2000, and while the numbers dipped during various market downturns, they keep coming back to roughly the same asymptote. The numbers are even more striking if you break it down further - the annual demand for personal vehicles has fallen by a factor of 4 since 1965, and by a factor of 3 since 2000, the difference being made up by increased commercial vehicle demand. Looking at other industries like steel paints a similar picture.