Dreadnought as a synthesis, not a bolt from nowhere

Were Dreadnought's components already available, with Fisher's contribution being to combine them?

Yes. Dreadnought brought existing cruiser design, turbine machinery, heavy guns, fire control, and construction experience together quickly and coherently.

A Dreadnought-like change normally emerges when someone combines several existing developments first, rather than when an entirely unforeseen technology appears. Fisher could build quickly because 12-inch guns were already under construction for the Lord Nelson class and because the ship drew on established cruiser design. A proposed 14-inch weapon would have required a more normal and slower procurement process, conflicting with the priority placed on rapid completion. Turbines, gunnery, rangefinding, hull form, and construction experience made Dreadnought both fast to build and historically transformative.