Depends on the group. Among the general population, that's probably true. Amongst the legal community, however, where I know there are minds that are orders of magnitude more brilliant than my own, I am an intellectual lightweight.
It's all a matter of scale in the group. There are times where I may be one of the more intelligent guys in the room. In law school and in the legal community, I can hold my own, but there are certainly sharper minds than mine.
Is Miers a brilliant person? Almost certainly; you don't get to be the White House Counsel if you are a dummy. Is she a brilliant lawyer? Probably. Is she qualified to be one of the top nine lawyers in the country, however? That's the million dollar question.
I've listened to the so-called glitterati, and I simply disagree with you. They ain't all that.
People are good at what they work on day in and day out. Give you 20 years of nothing but law 12 hours a day, and I'm gonna guess that you'll be able to spout it with anybody.
Some will depend on where you specialize. Go the political route, and I'll bet you get pretty fine-tuned in your understanding of the constitution.