The speed of a wave is determined by multiplying the wavelength by the frequency

We . . . that's not a very easy way to do it.  You'd still need
to figure out a way to measure the wavelength AND a way to
measure the frequency, so you won't find many engineers
actually trying to determine the wave speed by doing all of that.

But your statement is correct.  The product of

                       (wavelength) times (frequency)

IS the speed of the wave.

Rain is pulled by gravity which is a non contact force