I think if you transcoded all the music you want from Apple Music so that you could just listen with an MP3 player or PC of your choosing instead of their software, if you continued paying the subscription fee indefinitely - would be pretty defensible, ethically upstanding, and let's be real, there is a 0.000000000% chance you'd ever get sued for doing that on your own.

The hazards of course are that if someone were to do so and stop paying the subscription fee, they're in dubious moral territory, and if someone built a tool to "help" you do it automatically that person is going to be sued.