I agree, Lakadwala mentiond this in his book.

This is just a random thought about Capablanca, but as I learn more about his life, I am firmly convinced that ill health played a bigger role in his career than people realize. 

First of all, he really died quite young, only 53. He dies of a massive stroke brought on by Hypertension. He had previously suffered a mild stroke during the 1938 AVRO tournament in Holland.

Reading some interviews with Olga Capablanca, his second wife and his widow, it became clear that he had been treated for severe hypertension for many years. 

Based on this, I think the fact that Capa's play lost some of vigor later in his career might be due to a deteriorating physical condition. This might explain why his results became a bit more erratic as he got older. He would have indifferent results in a tournament and then turn around and totally dominate a very strong tournament just as he had in his youth.

These are just my own speculations.

I think as we grow older our mental capabilities weakens too specially when we are suffering from illnesses. In Capas situation, i think old age plus illness plus the rise of theoretically ready new GMs (Fine,Botvinnik, Smyslov,Keres, Euwe) made chess competition stiffer than before (not to mention Resehvsky and Kashdan, Horowitz, Stahlberg).Im a Capa fan and you can read that from my posts, but at 53 Capa was already not as superior as he was. I saw it while playing over his games in "The Unknown Capablanca", and "Capablancas 100 best games" not to mention lakdawalas' book too. And Paul...you are correct in your assesment.