All you are doing when you are recording a 'mix' from Spotify is illegally copying music made by other people that you don't own- so why should you have the right to share it? You haven't 'created anything. It's pretty terrible that so many people don't understand or care about that these days.
Amazon music let's you upload your own music and stream it from anywhere. There is nothing illegal about streaming your own music and there is no extra cost to do it. Amazon Music doesn't even really store your music, they match it song for song from their catalog.