Simplicity and collaboration

Leonardo didn't say that—it was William Gaddis in his massive novel about art forgery called The Recognitions, sometimes thought of as the first postmodern novel. In Leonardo's time "sophistication", had the concept existed, would have seemed like an obviously bad thing.

I believe it was Steve Jobs who popularized this misattribution, as well as the pseudo-Picasso one about how great artists steal (which really came from T.S. Eliot).

Edit: actually not Gaddis - after reading https://quoteinvestigator.com/2015/04/02/simple/ I think Gaddis might have been mocking the idea.