Grade inflation is always and everywhere an admission rate problem.
The US college-applying population has grown (a lot). The Harvard class size remains the same. Harvard continues to be a (the?) top tier school. This means that Harvard classes are probably getting better year after year. Even if Harvard is evaluating performance exactly the same (no new cushiness), if the admitted are better, they’ll be getting better grades on average, and those grades will be more compressed.
This would be great! My guess would be in 2022 the math is harder but literature easier.