I'm new to the Ebook game and confused about the ecosystem. Do Amazon, Rakuten, and Barnes and Noble really control the whole market? Anywhere I can buy big titles not from big companies?
For audiobooks, try Libro.fm (they can sell through or donate to your local bookstore).
Most (mega) publishers list their wares on their sites (e.g. Penguin) and will link out to where you can buy.
I think Apple Books has gotten better (fair) since they got slapped for price fixing on publishers. They’re also looking at AI generated audiobooks as an attempt to compete and pull market share away from Amazon/Audible, as far as I can tell. That’s good for the market perhaps but perhaps raises concerns for pushing not famous voice actor/narrators out of work. A concern about AI overall though, I suppose.
Anyway, my preference for either format is my library online. I recommend that option over anything else.
Have you checked the online stores of the regular book stores in your country? In Sweden I think both (yes, all two! Adlibris and Bokus) of the major book stores sell ebooks. For some titles they're actually better than the Kobo store (especially for classic books and nordic publishers I think).
Personally I'm happy with the Kobo store and Libby/Overdrive though. Anything that's not Amazon is fine in my book, and I really like that progress is synced between phone and e-reader for the few times that I don't have my reader with me.