For Mozart, composition was matter-of-fact. I have seen his original manuscript for the Symphony 36, 'The Linz.' It runs from first note to last note with barely an erasure or blot-out.
Not so, Beethoven, for whom composition was a herculean chore. In his original manuscript for his Symphony 3, 'Eroica,' there are holes in the paper from where he threw his pen in frustration, and great blocks of hastily crossed-out notes and edits.
Does this make one composer better than the other?
Not at all. Both Mozart and Beethoven are geniuses.
It's just that one had to work harder at it.