I really like Sherlock stories, but yes, they are seldom all that rational.

I remember in one story Sherlock concludes a man must be smart because his hat size is large. I mean, come on, even in Doyle's time this would have raised more than one eyebrow.

I don't hold this against the stories because my enjoyment of them is more about the mystery and Sherlock as a character, rather than they actually making rational sense.