If it were a canon/Victorian con, I'd agree with you, especially as that phrase does show up a LOT in Victorian-era adaptations & pastiches, including the Ritchie movies. Victorian Holmes unquestionably had it first. Victorian Holmes has every right to keep using it.

But it doesn't show up at all in Sherlock and that's what I'm reacting to. I don't remember Sherlock BBC using "elementary," much less "Elementary my dear John." They've named a Sherlock BBC con with the one word not associated with Sherlock BBC -- but identified with the other modernization.