And real nimby impact (as opposed to the impact imagined) scales much less than quadratic, because larger rotor implies lower rpm and rpm has a huge impact on perception. Small rotors emit a very strong "presence" when you are anywhere near, whereas the tallest ones feel as if they are on a different plane of existence even when you are standing right at the base. Certainly not quite as disconnected from reality as airliners passing by at cruising level, but it's a similar effect.

Thats linear scaling [1] so its still scaling quadratically. Ax^2 + Bx is a quadratic, after all!

(Also, shouldn't the first order approx should neglect wind speed as a function of height?)

[1] actually worse. From Wiki entry for "Wind Gradient"

"Although the power law exponent approximation is convenient, it has no theoretical basis.[18] When the temperature profile is adiabatic, the wind speed should vary logarithmically with height,[19] Measurements over open terrain in 1961 showed good agreement with the logarithmic fit up to 100 m or so, with near constant average wind speed up through 1000 m.[20]"