1. Overcast, great usability, terrible discoverability
2. Apple Podcast, bad usability, excellent discoverability
3. Spotify, ok usability, ok discoverability
The reason I have not unified on any one is these different trade offs and the low burden to having 3 different podcast apps. I only use Spotify for the Fantasy Footballers podcast and I can see myself unifying on Spotify if they became the sole distributor of a couple of casts I follow.
Which is to say, in practice, I do not share your conviction.