Although his solo and concerto compositions would forever fool you (pieces like Gaspard, the Tocatta from Tombeau, etc.), I don't believe Ravel--while he could play the piano somewhat decently--was a prodigy and certainly never accused of being a virtuoso in later life. But he knew how to write most artfully and pianistically for the instrument--in fact, better than many before or since. And he knew exactly how he wanted his pieces to sound and would willing and verbally coach artists like Marguerite Long and Vlado Perlemuter in producing those desired effects.
As another example, I never knew Moussorgsky to be a piano prodigy, yet he gave us Pictures at an Exhibition in its original piano solo form.
There were also composers who were not known as being prodigies on any instrument, piano or otherwise. I think, for example, of Charles Ives, an American icon, who arrived at composing later in life while he was the president of an insurance company, yet was able to push the musical envelope into directions of which nobody had ever conceived possible, and still boggles the mind today. So every now and then a mere mortal comes along who can change the landscape for us.
Then there were the opposite types--people whom we think of strictly as composers. One example is Prokoffiev. Yet he could toss any artist off the piano bench any day of the week to show him how to play the piano.