The counter-argument is equally simple: a sail is a surface. The earth is a sphere. A sphere made of solid rock the size of a sail will be even less moved by a 15 mph breeze than this hypothetical person.
Moreover, your suggestion seems to indicate that you’re only considering kinetic energy, which would be a very myopic and reductionist take on these matters.
The earth is NOT a solid rock. It's a very thin layer of rock, floating on top of a pool of magma, itself floating in space. The rock itself flows on all sorts of time scales as well.
A sphere will be forced by the wind, almost the same amount as any other object, regardless of its density or weight.
it's not a pool of magma, the mantle is basically solid
(except on very large timescales)