iHeart is currently the number 1 podcast producer by a mile. And Cumulus is #8. iHeart is also heavily invested in smart speakers (as is TuneIn) and bought Triton Digital which was one of the top programmatic ad networks for audio. I think this article was written at an inflection point and now that digital listening is exploding, they are riding that wave pretty effectively.

http://analytics.podtrac.com/podcast-publisher-rankings