> I can easily tell code written by a novice programmer naively 'vibe coding' an app from code written by an experienced developer using AI to help him. Can a history professor tell the difference between a purely AI essay from one written by someone who knows what they're talking about?

Yes. That you consider this a question worth asking is a sign of your contempt for the craft of writing an essay. If an AI is that bad at mimicking expertise in your field, why shouldn't it be that bad at mimicking expertise in others' fields?