I find myself disagreeing with Terence Tao (a very scary phrase to say!) and think the core question posed is whether the "misalignment" is between the mathematical community and humanity. In other words - are the Millenium Prize problems meant to incentivize advancements for humanity or foster the field of mathematics and mathematicians? As a counter example, if there was a prize for creating a drug that cured a rare strain of cancer, we would not care if it was AI that did it. We would be happy it has been solved. On the other hand, if long running agents figured out the puzzle in "Kryptos", the cryptographic statue in Langley, there would be something a tiny bit sad about the human artistry removed.