I agree whole-heartedly with this. I’m a die-hard Medium lover, both as a writer and as a reader as well. The fact that some content is gated to me as a non-premium member when I’ve exceeded my monthly “read” limit is mildly annoying, but not annoying enough that I want to spend money on it (even if it is just $5).
The reasons why I keep Spotify premium membership are because 1) I hate ads and 2) I like being able to have control of music (skipping, picking songs from a playlist to play).
If we translate this to Medium, I think that having ads on Medium would help sell their premium membership (that entails an ad-free experience) but also help Medium monetize itself even more since they can charge for that ad space. I do agree with you, though — have ads on a platform that distributes content is generally mildly to extremely annoying, even if served up as native content.