That was one of the reasons they killed the api: to support ad growth. Unfortunately they failed to realize the combination of ad-blocking browsers and users just quitting the site from losing client access means they were never going to hit pre-IPO revenue targets.

Had they instead focused on affordable API pricing and driving subscriber revenues up, they would have exceeded revenue targets.

source: I was in a somewhat similar position (not quite the same, no third party client), but chose different and found myself making more subscription revenue than ad revenue thanks to a viewer base more than happy to pay more.