This scene of Sherlock helping Watson adjust her vest reminds me of the scenes of his holding her coat for her, carrying her luggage upstairs, making breakfast, etc. Sherlock matter of factly takes care of Watson, not because she’s a girl, or needs help, or is dumb or weak but because he can. And I like the way she accepts the help with minimal to no acknowledgement, like she expects it of him. Its more than just friendship. Its the way one behaves with family - someone you are so close to that you can predict their needs and fill them without thinking and politeness doesn’t enter into it. It just is.
The dynamics of their relationship is master and apprentice but I’m not sure who is the master and who is the apprentice (cueing up Sting singing “Wrapped Around Your Finger.”)