Huh? You believe Marx thought up the Division of Labor theory?
Marx didn't invent capitalism, class, or division of labor, but he made good use of all of them.
Plenty of class struggle in ancient Rome and Greece.
It's been persuasively argued that Marx didn't invent anything, he just twisted other people's ideas and stood them on their heads.
I didn't say Marx invented the Division of Labor notion, but, as others have pointed out, he made extensive use of it and much of his thinking really hangs on the social differentiation which he said comes from the Division of Labor based on production.