Above: Sikorsky's X-2 helicopter in flight.

Without the imperative of a well identified threat there has been little political or bureaucratic interest in maintaining the technological advantage the West held over all nations in 1991.
At the end of the Cold War, the United States held a commanding advantage in most conventional rotary wing areas, with the Europeans lagging but closely behind, and the Soviets behind in all areas other than heavy lift helicopters.
At that time the US had two new programs in development, the V-22 Osprey, which was to herald a generation of new tiltrotor technology designs, and the RAH-66 Comanche Scout helicopter which was to have been the vehicle for new rotor technologies, and a very low signature or stealth design'
Two decades later the Comanche is 'dead' and the V-22, after a very painful and protracted development cycle, is only now achieving credible operational maturity. Most of the military helicopter types remaining in production in the US are derivatives or variants of Cold War era designs. Europe is faring better, as it has a generation of new rotary wing designs now in production, using composite structural materials extensively, but these vehicles are in aerodynamic and propulsion terms just as conventional as their trans-atlantic siblings. Much the same can be said of the latest designs in Asia.
In terms of mainstream production helicopter designs it would be fair to describe the area as largely stagnant. Most current helicopter production is intended to extend or directly replace Cold War fleets with like designs, at best with incremental improvements in performance parameters like payload range, life cycle cost or ballistic tolerance, and with more sophisticated digital avionics replacing the conventional cockpits of Cold War era designs.
Historically, rotary wing development followed two key lines of advance.