This. Based on several stories i've read (many you've named), i've always assumed Alan is a bit moody all the time(tho i'd like to think he's lightned up with time).
But it makes sense doesn't it? Alan got his powers in a terrible tragedy (survivor's guilt) + the fact that he's insanely powerful is enough pressure for anyone to be a tad pissy( there was A Batman Black and White story on s_d 1.0 that kind of hinted toward this).