The Contrasting Shapes of Genius

I am sometimes struck at the differing shapes of process among the great composers; for instance, in 1800, when Beethoven was about to enter his 31st year, his first symphony was produced and performed. Eight symphonies were to follow.
Mozart, in his 31st year, had completed all but the last half dozen of his 41 symphonies.
Brahms required between 14 and 20 years to complete his first symphony; the first of four.
Wagner sneeringly called Brahms "that prophylactic composer".
One of these days I'll relate to you what some great composers thought of others in the same pursuit - you will blanch!