The most informative grades would be uniformly distributed, it’s an opportunity for the geniuses to shine and give a signal to profs about who to hire for their PhDs.
If a class of 30 physics students all get an A, the value is in comparing their A to a B from another year or university.
The only function of giving everyone an A is to prevent shattering fragile egos who have never experienced setbacks before.
Unfortunately real life is full of set backs, so it’s better to learn to deal with it in a safe environment.
A common understanding of a grade is as an indication that the course material has been mastered. Higher grade = more mastery. This is a measure independent of the performance of fellow students.
If you gave a test out and the average was 99 percent, you would be ranking noise. They should make the course harder so even out the distribution of grades.
The most informative distribution (ie maximum entropy) of grades is uniformly distributed. The least informative is when all grades are the same.
There's a bald assertion here that lots of those professors would stop you at; that good grades and capacity for research work are the same (or even necessarily closely correlated).