<p>I’m not sure what you think the question of principle is here. </p>
<p>As long as all students have their grades converted in the same way, and the method is advertised in advance
and is not rigged to favor some students over others, there’s no issue of fairness, right? </p>
<p>Also, that Lucy and Desi switch places under the two conventions is meaningless, because any change in the details of the conversion system from letter to number grades (such as using 3.3333 and 3.666666… in place of 3.3 and 3.7) would shuffle the ranking of students around a bit, with implications for scholarships etc. You might find it more aesthetically pleasing to use the conversion that turns letter grades into a linear scale, but there is no issue of fairness to decide between one conversion scheme and the other.</p>