I'm surprised they don't just inject the ads directly into the video stream, I think that would solve their issue overnight (not that I want any ads personally). You could also rate-limit it to the playback speed to prevent pre-downloading the stream easily. But now that everything uses HLS/DASH, it's easy to inject different content right in the middle of the stream without re-encoding anything.
I pay for a subscription to The Athletic, who used to offer ad free podcasts in their app. Last month they signed an exclusive deal with Acast, and now I cannot possibly listen to their podcasts without ads.