One frequently hears pianists bemoan their small chops, but think of Joseph Hoffman and Alicia de la Rocha. They could do anything (well, okay, they sometimes had to roll chords that others could play simultaneously.) The point is that they could play everythng with surpassingly apparent ease.
To play with this kind of ease is an accomplishment, even where great talent is involved. To say that such apparent ease is a matter of coordination means, I believe, using your mind to employ whatever physical equipment one owns, and make it fit the problem at hand (so to speak....)
Within a certain range, I agree that the size of one's hands is not a big problem. Pianists who can't reach an octave are handicapped, to be sure. Pianists whose fingers are of too great a girth, or diameter, and can't slip their fingers between the keys are also saddled with a big problem, regardless of their hand span.
Pianists with exceptionally big hands sometimes have a more difficult time than those with smaller hands in negotiating convoluted, rapid-fire passage work. I'm not sure why this would have to be true, but an image comes to mind, as a matter of intuition: think of a big tennis player or footballer running full tilt and then trying to change directions rapidly. Maybe the big-handed pianist's issue of agility here has something to do with mass and inertia. Or maybe the relation and dynamics of finger to key. Maybe something about the ratio of finger to key size.
The actual proportions of one's hand may be a bigger issue. For example, it's a problem if one's thumb is not long enough, in comparison to one's other fingers, because, for one thing, this configuration tends to make the remaining fingers cramp up into an unnaturally tight curve; imagine the shape your hand makes when all one's fingers play with the fingertips in a straight line on adjacent keys. If the thumb is too short, it cramps the remaining fingers. A similar problem happens if one's 5th finger is too short, especially when compared to one's 4th finger.
One's mind is the bigger issue, the manner in which one brings reason to bear on the problems at the keyboard.
Best regards,
Eric Nolte