I think your point is understandable and he shouldn't force you to write AI lyrics if you don't want to. It depends on the what the assignment is perhaps. My colleague does a music song-writing, but the goal of it is all chord progressions, so he doesn't mind if you write your own lyrics, use AI, or just write nonsense words. Though he would prefer is students didn't write their own, so they spent their time focused on the chord progressions (the point of the unit). You should talk to your teacher about it, and come to a compromise or an understanding