If they had stuck with that, it would have been a great homage to classic sherlock holmes. I am not sure the writers needed to make it more complex with the Moriarty and mind palace subplot.
On the one hand, I can see how it could've been interesting to see how the show's staff would handle "classic" Sherlock Holmes. But on the other hand... tons of people have already done classic Sherlock Holmes. What more is there to add to that? It would've been kind of going through the motions if that were all they'd done. They chose instead to have a dialogue between classic and modern Holmes -- which is what they've kind of been doing from the word go, but it was more overt here. They took classic Holmes and used it in a new way, not just imitating it but commenting on it and interrogating it, remixing it as a modern Sherlock's projection of himself back into the past, with its familiar elements gaining new meaning as representations of Sherlock's mindset toward himself and the people around him. And it critiqued and deconstructed the gender norms of Victorian society in a way that a straightforward adaptation could not have done.