I find your comment helpful insofar as it points to ways in which my article might be misunderstood, but it would be more productive to be inquisitive.

So it's not like they indicate an actual mental deficit

No, I think that his verbal abilities are significantly above average relative to the general population, but perhaps only average relative to mathematicians as a group.

Given that, I don't see why we should expect a "still lower ability" anywhere

Do you know principal component analysis?

My point was that the SAT verbal is that surely partly a test of abstract reasoning ability of the type picked up on by Raven's Matrices, while partly being a test of a second thing, so that performance on the SAT verbal is determined by a weighted average of these two things, and that since Tao is really high on abstract reasoning ability, he must be lower on that second thing than his score would suggest if taken in isolation.

My impression from reading TT's blog is that he has rather a lot of useful things to say about thinking techniques; see e.g. lots of the links from here. He doesn't strike me as someone with "relatively low metacognition" unless you mean "low relative to his skill as a mathematician" (in which case: well, yes, but I don't think that's an interesting observation).

Yes, these things are all relative. I added an edit to my post to clarify. For the most part, I find Tao's comments on thinking techniques and his advice sound. But there are other elite mathematicians whose understanding runs much deeper, and this is in fact highly significant, just as it's highly significant that Tao was able to score 760 on the math SAT at age 8 rather than at age 13.

It's possible that TT has made an error here -- that exceptional IQ-style intelligence is more important to mathematical success than he thinks it is -- but I submit that "poor metacognition" is probably not the best analysis of why, if so.

Do you have an alternative explanation to the two that I proposed? Surely you'll concede that there's something a priori very bizarre about the situation: Scott Alexander, who got a C- in calculus, is able to recognize a simple quantitative argument that one of the best mathematicians missed, despite the fact that Tao is much closer to the situation that Scott is analyzing than Scott is.

I think the analogy is flawed in an important way.

I agree that there's some asymmetry, but I don't think that it's relevant. The point that I was getting at is more subtle. It's clearly not true that Tao and Portman were only successful because of their intelligence and looks respectively. I think that a careful reading of my paragraph will make my meaning clear, but if not, I can try to clarify.