This is also reflected very clearly in EA Survey data.
Here’s the breakdown of which specific podcasts people cited in EAS 2020, for where they first heard about EA.
You can also get a sense of the magnitude of Sam Harris’ podcast compared to other things like Doing Good Better from looking at the total number of mentions across response categories. (Respondents were asked to first indicate where they first heard about EA from a list of broad categories like ‘Book’, ‘Podcast’, and then asked to provide further details (e.g. what book or podcast) in an open comment. Only 60% of respondents to the first question gave further details so the numbers are commensurately lower.)
Taking these numbers at face value, Sam Harris seems to represent more than twice the recruitment effect of Doing Good Better, and slightly higher than half as much as Peter Singer.
One good reason not to take these numbers at face value is that they will be influenced by how recently these factors were recruiting people. We see consistent signs of attrition across cohorts, so a factor which recruits people in 2020 will have a lot more of those people left in the sample than a factor which recruited a lot of people in 2015 (of whom probably >60% have dropped out by 2020).