> This is just benchmaxxing.

I believe the normal term is "gaming a benchmark test".

Nothing in what you quoted is related to that. It's a normal way to train and test a classifier.

The only way to determine if it's brittle is to test on a different dataset and look at the sensitivity and specificity.

Even so, there is nothing wrong with a model that is trained to a narrow domain when it doesn't need to deal with "wild" images.