I can only see that being kinda true on a technicality since modern literary heroes are probably hard to find in fiction before the development of popular adven

I can only see that being kinda true on a technicality since modern literary heroes are probably hard to find in fiction before the development of popular adventure stories and, thence, genre fic, which was still pretty young when Holmes came around. Plenty of protagonists known for their intelligence before then. Often even just for their intelligence, not tied in with a ton of other gifts. They just had a tendency to be, you know, tragic. Less with the triumphing-against-the-odds of modern literary heroes. Daedalus, say, to pick a fairly old one. Gonna have an even harder time finding the triumphing-sort coupled with capital-S Science or capital-I Invention much earlier than Holmes, for obvious reasons. Clever characters are all over folk tales and such, of course, deducing left and right and triumphing often enough, but they're not gonna be Holmes. You need science—scientific police investigation, such as it was then—plus the modern literary hero, for that.