Typing people is always an art, not so much a science. Individual personalities are so diverse and dynamic that it is impossible to sort people into 16 groups without exceptions. With fictitious characters it can be even more difficult because you cannot get direct contact with them for analysis, everything is drawn from what is given up front.
Here’s a plug for Sherlock as an ISTP rather than an INTP
Holmes is an ISTP. Many people assume he’s an N for much the same reasons that real life ISTPs sometimes mistype themselves as INTPs. Dominant Ti can seem like intuition, when what is really happening is determination of cause and effect and making logical deductions, and not connecting seemingly unrelated dots to form a bigger picture. There’s a huge difference.
You don’t need intuition to make connections, if the effect you’re seeing implies causation. For instance, if you find an egg then you know there must have been a chicken. When Holmes noticed knife scrapes on Watson’s shoe, he deduced that Watson’s servant girl is clumsy and that he was wet recently. He figures this out because the scrapes imply someone trying to remove something, and mud is most logical. Further, he knows that since Watson is a doctor he would have a servant girl clean his shoes. The visible scrapes implies carelessness. Mud implies being out in the rain. All of this seems mundane and obvious when reasoned out, but when you walk into a room and Holmes tells you you were wet and have a careless servant girl, you would probably be impressed since you’re in clean, dry clothes and your servant girl is safely locked in her cage at home.
Holmes’ gift of deduction is merely realization of the causes of effects that wouldn’t occur to other people. He does this mostly by having an extensive catalogue of knowledge in various subjects he deems relevant to detective work. In fact if we look at Watson’s assessment of Holmes’ knowledge, we see someone who is very practical and uninterested in theory and subjects not directly relatable:
Knowledge of Literature — Nothing.
Knowledge of Philosophy — Nothing.
Knowledge of Astronomy — Nothing.
Knowledge of Politics — Feeble.
Knowledge of Botany — Variable. Well up in belladonna, opium and poisons generally. Knows nothing of practical gardening.
Knowledge of Geology — Practical, but limited. Tells at a glance different soils from each other. After walks, has shown me splashes upon his trousers, and told me by their colour and consistence in what part of London he had received them.
Knowledge of Chemistry — Profound.
Knowledge of Anatomy — Accurate, but unsystematic.
Knowledge of Sensational Literature — Immense. He appears to know every detail of every horror perpetrated in the century.
Plays the violin well.
Is an expert singlestick player, boxer and swordsman.
Has a good practical knowledge of British law.
An INTP would study anything interesting inside and out regardless of its worth to his work, and his interests would be more varied than this. Instead we see he knows “nothing” about esoteric subjects and only “practical” knowledge of subjects vaguely related to detection. He has “profound” and “immense” knowledge of chemistry and sensational literature only because they greatly help him deduce the method and modus operandi of his subjects. His knowledge of anatomy is “accurate, but unsystematic” because it helps him determine the cause of death as well as events leading up to the moment of death (e.g. if there was a struggle, etc.), but an INTP’s knowledge would probably be something bordering on “systematic.”
Finally, his secondary Se is the second part of his great gift. When you think of Holmes you think of his brilliant deductions as well as his attention to detail. He’s a guy who walks into a room and within milliseconds he is aware of the position of everyone and everything in it and can spot a speck of dust on a pair of brown trousers. He is keenly observant, is what I’m trying to say. Point to me one INTP that can find an elephant in his living room.