This does of course raise the possibility of a scenario in which a higher risk design approach might be preferable to a lower risk one because the higher risk approach has much more detectability, and a present professional user would mitigate the harm. I would suggest though that in that scenario, the analyzed risk remains higher, and acceptability of the detectability-based design approach is a deviation from the normal procedure and would require documentation of why it can and should be accepted.
But please note that, in the case of the user (being it professional or not), you do not to go thru the usability engineering process to make sure that he can do what is expected. The problem is blindly relying on the professional user - the problem might be with the device design, which induces use error.