So a magnum opus is solely on lyrics?
mag·num o·pus
ˌmaɡnəm ˈōpəs/
noun
noun: magnum opus; plural noun: magnum opuses; plural noun: magna opera
a large and important work of art, music, or literature, especially one regarded as the most important work of an artist or writer.
Most important work of artist. I think Loud qualfies as most important but id say same about GGGB