Nothing new. Some older adults have always assumed that. I heard it when I was a kid.
And in some cases, in some school districts, some kids are getting a dumbed down education. But not all kids, and not in all districts.
...when I changed High Schools between 10th & 11th grades (family moved), I was astounded by how... easy my new school was. Suffice to say that I thought then, and I think now, that they didn't push the kids very hard in that district. Now, maybe it was a little more maturity from me at the time, but my younger brother went through the same thing. I went from a middling-B student to an A, and he went from a barely-C student to a high-B/low-A.