But that's absolutely not generative AI (which bandcamp explicitly stated the policy is for) and it's not even classifiable as traditional AI. The session tracks are just some base patterns selected by sliders attached to options adjust stuff like "play these notes in an inverted chord".

Hmm, a few years ago, such a feature would have been called "AI" in marketing materials, no? Aren't all current GenAI tools in some way "just some base patterns selected by sliders attached to options adjust stuff" - only the 'base patterns' are some weights in a neural network.