If you're going by grades, then odds are what you're really selecting for is students who are good at the things they felt safe taking, not those who challenged themselves.
My university colleagues who got straight A's were mostly mediocre but had very good memory, learned only what was needed for the test, and occasionally cheated. Most of them didn't understand how things worked, but they memorized everything possible.
On the opposite side, I had colleagues who passed some courses with flying colors (sometimes going so far as to being exempt from taking the final test due to their prowess during the semester), but failed other, unrelated courses, because they simply didn't care.
On the opposite side, I had colleagues who passed some courses with flying colors (sometimes going so far as to being exempt from taking the final test due to their prowess during the semester), but failed other, unrelated courses, because they simply didn't care.
From my experience, I have zero faith in grades.