Good point with QBs. I have a theory. Not claiming I'm a master football tactician and that it's right, but here it is:
A QBs job is to read the defense. All of it. He has to keep track of the formation of the defense, what type it is (zone, man, etc), assign the mike, and so on. I think this favors a more analytical, down to earth mindset, like you said.
Whereas a DB usually only has to beat their guy. Especially if they're running a man-to-man defense, the DB focuses on beating the guy they're assigned to. Imo this favors a more cocky/confident attitude, "yeah, I can beat this kid no problem... easy!"
Anyway that's my theory, not saying I'm definitely right and you're definitely wrong. Just what I think.