Once you put your podcast onto Spotify they give you better info on your listeners and subscribers and number of listens (at least the ones listening on Spotify). You don't lack any data.
We've refused to put any of our 8 podcasts on Spotify for various reasons. One of the reasons is that they will accept money from paying customers and from ad co's for non-paying listeners, but simply want our content for free. Ummm... no thanks.
However, Overcast also caches RSS feeds but it does send the number of subscribers for a feed in the header of the GET request. It also doesn’t cache the actual audio.