I'm a first year PhD student and I randomly go to different professors' websites to admire their works. Usually an economist has around 20 published papers when he/she reaches professorship. But there are a few outliers, like Andrew Lo, Darrell Duffie, Kenneth Singleton and Paul Samuelson, who have like a few hundred of papers published. Are they simply more productive than others? Is the number of publications (of course above a certain standard of quality) a good indicator of the economist's ability?
A short answer to your question is both yes and no. You have to first define productivity: productivity, in my opinion, cannot simply mean publishing the number of articles, but rather, their impact. A typical way of modelling the impact of authors is by looking at their h-index. There are many other ways of measuring productivity as well- where the articles are published is important as well. The top 5 journals in economics are (in no particular order): Econometrica, AER, QJE, JPE and ReStud. Articles published in these journals are generally of high quality. However, there are many articles that are published in these journals that do not always have the desired impact. Many a time, articles ranked in lower journals have a high impact. Consequently, it is extremely difficult to measure productivity. To me, the h-index is a good measure.
Another aspect is a little bit about network effect. Suppose for a one moment that there are two researchers, one in USA and another in Asia, having both the same paper, do you really think that two researchers have the same chances to publish in Econometrica or in another top journal ?
So, the term of productivity is highly biased by this network effect. It is a little bit close to ChinG's response. People not having chance to publish a very good high impact paper in Econometrica, publish in another good journals like Journal of Economic Dynamics and Control, Journal of Economic Theory and etc. For me, a guy publishing in Econometrica being in Europe and another guy in USA with an Econometrica paper are not same.