It seems you might have different assumptions on who works which jobs. Factory workers span the whole range of people who are great at thinking and people who are bad at thinking. So do scientists/engineers/doctors. I don't think I would agree that only those "who are worst at thinking use AI the most", but if it were the case, then evidence that scientists/engineers/doctors are the people using the tool the most does not invalidate the claim. It could just means that those who are in those jobs and are bad at it are also the ones using AI.