NEW HAVEN, Conn. — Nearly 80% of all grades given to undergraduates at Yale last academic year were A’s or A-minuses, part of a sharp increase that began during the coronavirus pandemic and appears to have stuck, according to a new report. The mean grade-point average was 3.7 out of 4.0, also an increase over pre-pandemic years. The findings have frustrated some students, alumni and professors. What does excellence mean at Yale, they wonder, if most students get the equivalent of “excellent” in