I have heard several of Salieri's overtures, and have to say that there are quite good. He repeats the same theme many times, but the themes are charming and delightful. Salieri gets a bad wrap. Not the calibre of a Mozart, but certainly a gifted composer who deserves to be celibrated for his contributions to the great western musical tradition (not to mention his role as an instructor).
"He repeats the same theme many times, but the themes are charming and delightful."
That was a standard practice of most composers of those days.
And I've forgotten which part of the Requiem it is, but it is clearly a re-use of "And With His Stripes We Are Healed,"
from Messiah by Handel.