I have never used the app. Like you, by the sound of it, I find Amazon Music user unfriendly and I have little interest in it.
I have, however, purchased many albums from Amazon which came with AutoRip. I find I can still see and access these by going to “My Account” on the Amazon website, then click on “Your Music”. Then there is a “Library” tab at the bottom which enables me to access all of those AutoRip purchases. So, no, for me at least they have not disappeared. I never really listen to them though !