Since the OP hasn't replied, here's how "I" would define a Major Composer: someone who is capable of writing music in a variety of musical contexts, with a variety of instrumentation, AND whose music is (has been) performed by multiple performers on a broad geographic scale.
So following this criteria, someone like Ferdinando Carulli is a Major Composer: solos, duos, duos with piano, duos with flute/violin, and full concerti. Mauro Giuliani and Anton Diabelli as well. Fernando Sor? Certainly: just because the ballets and masses he composed haven't survived the centuries doesn't mean they didn't exist, and the published critiques of his era show they were well-regarded by his peers.
In the 20th century, the "Segovia Composers" were all well versed in writing music for many different instrumental or vocal contexts. Ponce, Turina, Torroba, Tansman, Castelnuovo-Tedesco, Mompou, Rodrigo, Villa-Lobos all have a much wider musical output than just their guitar music. And the "Bream Composers" such as Britten, Walton, Berkeley, Tippett, Rawsthorne, all go one better, being much more recognized on the global musical platform for their non-guitar music than for their sparse but important guitar pieces.
I am hoping the OP comes back with his/her own criteria for a "Major Composer".
Salt Lake City, UT