This advice is based on having written a few books and having an agent. I agree with others that you should ignore this interaction as feedback on your ideas. Or maybe to be charitable, to chalk it up to a misunderstanding.

Some agents want to invest and work with new authors to build a good book proposal together, based on the fact that they know the market and they want to nurture you into becoming an author.

But others are simply willing to randomly email someone who writes well to see if she or he has a fully worked out book proposal ready. She sees herself as polishing the proposal, setting up meetings and selling the book.

By metaphor, #1 is like someone who comes upon a promising site and wants to help build a house and sell it. #2 wants the house to already be there.

So obviously you ran into agent #2 instead of #1. The fact is that while all of your proposals have promise, they aren’t what #2 would think of as a book proposal; they are what could become one.

So the mistake is to take this as feedback as to your potential as a book author.

But it does suggest that in your free time outside of Medium you might want to try turning one of the above ideas into an actual book proposal, including an introduction to the book, a table of contents and sample chapters (all of which is very unenjoyable frankly). It is a painful process, but trying to do that often forces you to think hard about what might work as a book and what might not.