more generous grading than usual, in line with results from summer 2020, so that this year's cohort is not disadvantaged
By extension that means that other cohorts are disadvantaged. If they said the same grading as normal (which is how they normally sort the grade boundaries).
If you make it easier to get a grade in one year, that either means that in the future people will dismiss those grades as unearned, thus disadvantaging those students or people will compare others and disadvantage the other students.