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You are SO wrong!
While there is some of that in some of his music it is not in his choral music, it certainly isn't in the Requiem. There is nobody who could do variations on a theme better than Mozart, he would have loved Jazz. The style of the day was to have themes in music and to modify the themes without repetition was a difficult thing to do, he did it best. Variations on a theme may sound like formula music, like computer code perhaps, but, it is not that simple. When Mozart did it he often changed not just the time signature but often key and not a simple change of key, often from major to minor and then back. To listen to Mozart's Requiem is to be lifted into Heaven for a few minutes.
Then by all means, lift yourself. (Sorry, it's not the Requiem.)