I went to mass in Stephansdom yesterday. I´m old enough to remember before Vatican II when masses were musically interesting, and was relieved to see the ordinary was a little mass by Michael Haydn, Franz Josef´s older brother.
Called the Heironymus-Messe, it dates from 1777. The unusual feature of this mass is that there are no strings, just oboes, bassoons, trombones and continuo. It is a symphonic mass, which means each mass section is a single movement with solos integrated into the choral texture. It is a sweet little mass very much in its period. The music was done in Latin and the rest of the service in German.
Michael Haydn is considered neglected. Lots of people are neglected. The vast majority of composers are neglected. The giants composed in contexts created by others.