I think it's only obvious when very little care is put into its use. If you just dump the homework in and paste in the output, it might seem suspiciously uncharacteristic. However, if you use specific prompts to generate specific parts of the thing you're trying to write, at some point you can make it totally plausible that you wrote the whole thing.

I should hope that a good writer would have enough artistic integrity to use it for ideas, but still construct all their own sentences.