The brain is dumb and as untrained as a muscle that never got exercised, until the brain is trained to use its neural networks to perform tasks that are put to it. Not tasked to do certain things the brain is hard pressed to address a mental task put to it and the person says, particularly in math and logic - “I don’t know”. I am not better at math because my brain is better at math. I am better at math because a few great teachers and I imposed more and more difficult mathematical tasks for the brain to do. In the analogy of a well exercised muscle the brain got stronger.
If people no longer know how to judge an A.I. result, as simple as with math, A.I. becomes more than a “tool”, it is a brain for its human robot it feeds instructions to.
I’m not sure I follow everything you’re saying, but I definitely agree with your “brain as a muscle” metaphor. I love math and still start my day with brainteasers. If I skip a few days, I can feel the difference—my thinking gets sluggish.
As for AI: if a person stops using it as a tool and starts letting it do their thinking for them, they’re basically surrendering their brain. Will that happen on a large scale? I don’t know. I’d like to believe some people will resist the temptation to become slaves.