While one can now edit and delete ActivityGenerators (and Projects) from within the main UI, the underlying ActivitySets are unobvious.
I don't really know if these need more exposure (and are available in Advanced Administration) but it might be helpful to make them explicit to help admin users realise that activities have been generated, and to delete them on mass if done in error.
Plus, deleting an ActivityGenerator or Project will cause a cascade deletion, so worth considering.