Maybe you can share those other sources, since quick search in storytel did not give most of the stuff I'm currently reading/listening at the moment?
I have been thinking about not selling my soul to Amazon, but the amount of books (and formats) is just so convincing. I usually read & listen at the same time, depending on time of day and being able to get everything from one place is just something that makes one problem less in crazy days, which seem to be the norm recently.
I personally use libro.fm. They have a lot of things that aren't audible exclusive, but not everything sadly. Also no non-English content
I have realised the no service will have all the books. So why not pick one that has more local authors and comes from a company that treats their workers and authors a bit better?
I don't see how any competitors could break their dominance as long as the authors give in this easily.
I listen to audiobooks quite a lof and some yeargs ago I moved to a different service (storytel, its a European thing). If they don't have a book, well I get it from another source that is definitely not owned by Bezos.