I don't refute the findings but I would like to mention: without AI, I wasn't going to be writing anything at all. I'd have let it go and dealt with the consequences. This way at least I'm doing something rather than nothing.
I'm not advocating for academic dishonesty of course, I'm only saying it doesn't look like they bothered to look at the issue from the angle of:
"What if the subject was planning on doing nothing at all and the AI enabled the them to expend the bare minimum of effort they otherwise would have avoided?"