Nose down in response to an upward gust is good; nose down in response to airspeed is bad.
But we are dealing with two different and unrelated phenomena.
An airfoil has an aerodynamic center where all aerodynamic forces can be considered to act. For normal airfoils, this is at ~25% of chord behind the leading edge. Nearly all rotorcraft utilize airfoils mass balanced about the aerodynamic center. A gust produces no pitching reaction.
A tail heavy airfoil, one having mass balance at a point aft of the aerodynamic center, produces a nose up twisting torque when subjected to an upward gust. The gust acts on the aerodynamic center and inertia does the rest. Such an airfoil is unstable vs. angle of attack. Mildly underbalanced, such a rotor produces the feel of a balloon as described previously. Strongly underbalanced, flutter is likely.
A nose heavy airfoil, one having the CG forward of the aerodynamic center responds in the opposite manner. An upward gust tends to twist the airfoil nose down, alleviating the effect of the gust. A cyclic pitch input is no different than a gust. An overbalanced airfoil responds at a lower rate than an exactly balanced airfoil, producing a heavy stick.
Bensen in one of his experiments, over balanced a wooden rotor to the extent that it would not respond at all to a cyclic input.
This is easily explored with an electric drill and a strip of thin sheet metal to mimic a rotor. Aluminum flashing material, ~0.010” thick works well. Run the drill backwards to avoid unscrewing the spindle bolt.
Cut a strip of thin sheet metal about 1” wide x 12” long and run in your electric drill. Without nose weights, it will flutter violently. Single nose weights will probably prevent flutter. As the amount of nose weight is increased by adding more nose weight screws, the “rotor” will respond more and more slowly to the tilting of the drill motor.
A rotor with a nose down aerodynamic pitching moment is bad in that it tends to run away with airspeed. The faster it goes the greater the tendency to twist nose down.
Bensen wooden rotorblades had excess reflex and a nose up tendency which increased cyclic flapping and added to velocity stability. Not necessarily a bad thing because it limited top speed; a Bensen with wooden blades would begin to run out of forward stick travel at 60-70 mph. Additional power would cause it to climb at the same airspeed. My first Bensen with wooden blades didn’t require a trim spring for hands off flight at 45 mph.