I don't follow your logic. First of all out of 21K followers, assume that at least 50% don't really care about your content, they just follow and then disappear for ever. The following tab of the feed is perfectly useful and accessible, UNLESS someone is following hundreds of authors and publications, but there is no design solution for that.

Finally, it's safe to assume that many who claim not to have seen your content are just being polite and trying to find excuses.

I did not say the email feature was pointless, just that anyone who subscribes to get emails from you, has to prioritise you over many others, because subscribing to hundreds of email is unsustainable.