Like, Elementary’s Sherlock and Joan are coming from a completely different place and have built up their relationship on completely different terms than BBC’s Sherlock and John. You can’t substitute one speech for the other and have it have the same meaning without the context behind it, despite them all being different versions of the same characters.

Elementary’s Sherlock and Joan are both starting off from their lowest points personally and career-wise. Their relationship is entirely professional and strictly conditional at first. For them to both independently recognize “hey, this person makes me feel happy and fulfilled in a way I haven’t for a long time” is significant because it’s admitting to a shift in their relationship, from professional/conditional to friendship and a mutual acknowledgement of “hey, I do actually like spending time with you even when I’m not obligated to.”

BBC’s Sherlock and John are never really obligated to spend time with one another. From the beginning, John chooses to accompany Sherlock, Sherlock enjoys John’s company (and the ego-stroking that comes with it) and their friendship forms pretty fast, even if it takes a whole season and a half to say those exact words.

To give this version of Sherlock Elementary!Sherlock’s speech to Joan would ring false because there aren’t sixteen episodes worth of buildup to this point with their characters. There isn’t a need for an acknowledgement of a shift in their relationship from professional to almost familial because BBC Sherlock and John didn’t have that same journey and were already friends by the end of episode 1.