yes, you are both right in this aspect. But just think why is it Mozart the hardest perform then? if you say bacause of transparency and accuracy of notes, well...under this line it could be also Haydn, Corelli, Scarlatti, Soler.... and the other neoclassical composers born after or even the serialists, dodecaphonist or whatever music is just pure. You can´t miss a note there too! right?
Mozart is somehow a mistery we performers have the duty to solve. And this mistery is not placed only in the notes. Believe me, mates.