And I have to say I'm kinda surprised at the recent change from Watson being Sherlock's sober companion to now being a "junior detective." Clearly it was in the plans all along, but it does seem like a pretty big shift in the show's concept.
Well, they've been setting it up for quite a while, so it's hardly out of nowhere. We learned some time ago that the companion gig was supposed to be temporary. We had a whole arc of Holmes being impressed by her potential as a detective and encouraging her to embrace it. We had 2-3 weeks of people telling Joan she seemed happier with the detective stuff than with the companion stuff, and Joan resisting it. And once M. Holmes terminated her employment and she stuck around anyway, it was clear that that would be a temporary situation and something would have to change.
So not so much a recent big shift as the culmination of a process that's been building up for months.