And Mr Darcy? And Howard Roark? Aren't they a great characters?
I can't see Mycroft as a person caring about details, he is concentrated on the outcome.I'd definitely say Mycroft is an INTP.
Sherlock is better at making judgements, whereas Mycroft is much more thorough about the details.
That actually sounds more Ti than Te to me .This is exactly what INTJs do. Not all of us are 6s, some of us are 5w4. INTJs are obsessed with patterns and connecting them and contextualizing them. This is what I'm constantly doing all day long.
Also he is more process oriented. It’s solving the puzzle that matters, helping someone is additional benefit. And he keeps repeating Watson to look at the problem from different perspective and then they will understand it. That all sounds more INTP than INTJ. I think that INTJ would be concentrated on the solution of the problem and not process of solving it. I think Te is more organized, more basing on deduction, where Ti is basing on deduction and induction. But the last one is my own theory