I think that it is worth differentiating between a theme park and an amusement park.
While I would personally rather ride BGW's coasters than most others, including anything at KD; I don't think the park has historically tied itself to a single ride as its draw. I'm not saying they don't build the "biggest, fastest, tallest, whatever-est" to draw people in. But I am saying that unlike places like Carowinds, they have other -- possibly equally important -- draws for guests.
BGW and Dollywood, in my opinion, are closer to Disney and Universal on the spectrum than a traditional amusement park. The environment, theming, animals, shows, and other attractions are designed to create a cohesive package. They are not promoting themselves as the park that owns El Toro; they are telling people that they will enjoy every aspect of their Busch Gardens experience.
So, I guess my point is that I'm not sure that even if you accept the premise that neither Apollo, nor Nessie, nor Alpie "put BGW on the map" (which I don't), that it naturally follows that BGW needs a Fury-equivalent to draw in guests. It certainly isn't all that they need. (No, I am NOT saying they don't want a record-breaking, nationally-acclaimed coaster; I am saying that here is much more to their product than a great track layout.)