Complex sentence: It became much less clear later who amongst performers and writers were working class, with workers commonly describing themselves as middle class (a term Karl Marx used for employers) and most songwriters of working class songs working outside of what was once'industry'.
Split into simpler sentences: It became much less clear later who amongst performers and writers were working class. Indeed most workers came to self describe themselves as middle class (Marx used this term for the employers) and most songwriters of working class songs worked outside of what was once'industry'.