The Books and Publishing ecosystem is in a state of constant change. You cannot rely on just 1 group of Clients because
1) You don't know how long they will be around
2) You don't know if they will continue to be successful and keep buying your services

Please read the Path 10 Page - https://review0.com/author/service-providers-start-here/pages/path-10-i-want-a-reliable-supply-of-trustable-author-clients-who-dont-try-to-take-advantage-of-me-with-spec-work-and-free-trials.php
That page discusses building a Reliable Supply of Trusted Author Clients
We strongly recommend that approach i.e. Building 3 separate streams of Clients and constantly growing your Client Base

Of course, we'll add some more context to why we think it's pointless to focus on just one group of Author Clients


What happens in a normal, healthy ecosystem -
1) The early movers build brands and benefit from the rapidly expanding market
2) These early movers keep getting stronger
3) There are new people that keep coming into the market. The good ones establish a customer base and become strong
4) As the ecosystem grows and evolves, the best people and the earliest people keep growing stronger

In that idealistic scenario, it makes a lot of sense to focus on one group of successful authors

Unfortunately, Books and Publishing is not such an ecosystem. Here, all the large companies (both old guard and new guard) try to kill off all successful authors and companies

They use all sorts of means to make sure that the earliest authors and the best authors cannot become so successful that they become self reliant and don't need the bookstores any more

Instead of merit and early mover advantage, the store bestseller rankings and book sales are based on 'Divide and Conquer'. The aim being to keep all authors small and powerless

You simply cannot survive if you base your success on one particular group of authors, as the stores and large companies are constantly killing off successful authors


There is another huge risk with relying on one group of authors. The stores might not be able to succeed in wiping out the authors that are becoming successful and self-reliant. However, they can add a lot of speed bumps and limit the earnings of such authors

These 'on the verge of big success and self-reliance' authors, no longer have as much money. They can no longer afford your services

The constants in this ecosystem of Chaos and constant change are
1) The large players keep wiping out successful authors
2) Those they cannot wipe out, they limit and stunt their growth
If you make yourself depend on one particular group of authors, you are guaranteed to be left with very few customers

It's incredibly risky to base your success on how one particular group of authors does. Unless your client base are Big Publishers or Top 20 Authors (in the entire world, across all genres), we very strongly recommend not putting all your eggs in one basket