I wonder if this kind of test would show the same results if you compared people using calculators for math problems vs. those without. From the basic operations to doing trig and calculus, if you provide an easier way they're going to take it, and unfortunately not going to pick up on how the answer is obtained, which an LLM will usually tell in the process. Doing something yourself always teaches you better than watching it, or just being told the answer.
If the tests are implying or showing that people who already were proficient in doing these tests and would have done well without started declining after exposure to an LLM's help, and that persisted... that's a different problem and one that should be looked into. Losing skills you had because of help? That shouldn't happen.