The issue with audible is that authors have to be there or they don't exist. Even if the pay is crap, you "have to" be on audible.
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.