That's not evidence the tests are flawed. I was just having a very similar conversation with a friend who aced the physics olympiad. She said, "it's too easy to game, all I had to do was try old tests on my own". Well, hundreds to thousands of others were putting in more hours doing the same thing, in addition to enrolling in expensive prep programs, and they didn't do as well as her.

That is evidence in favor of the test's quality, not against it. There's no paying to win.