The Mona Lisa is not the best artwork ever, and as a painter I am not sure Leonardo is much better than either Mantegna or Piero della Francesca, neither of whom is much known to the general public, much less Titian. He has no work as stunning as Michelangelo’s David, and too many of his commissions he left unfinished or he never started them. The Notebooks display a fertile imagination, but do not contain much real knowledge of use, except on the aortic valve, nor did they boost gdp, nor are they worth reading. Much of his science is weak on theory, even relative to his time. In Milan he was too content to serve as court impresario, and he seemed to have no idea of how to apply his own talents in accord with comparative advantage.
His ability to take an idea and turn it into a memorable sketch was his most remarkable ability, and in this he is without peer.
Plus he painted “woman as gorgon” very very well, but with a sweetness too.
I can recommend Walter Isaacson’s new book on Leonardo as a wonderful introduction, but it does not change my mind on these points.