In my daily life, I hear about books more than visual art and I run a gallery space...so I have a little trouble accepting the generalization that Tolstoy takes a back seat in the popular imagination to DaVinci. This may be true, I'm not sure, but the relative prominence of one form over the other is not universal.
Outside of the popularity issue, the question of which form of art is more expressive is an interesting one. Literature seems to be more fully and specifically articulate of ideas. Visual art may be capable, in its way, of representing a more direct translation of emotional experience than literature.
For sake of conversation, I'd distinguish the two forms in this way, saying that literature offers a greater fullness of expression while visual art offers a greater immediacy of expression.