The problem is that the 'middle class' doesn't exist. It is a series of cultural affectations, that do not apply to the majority that supposedly make up 'the middle class'. If the 'middle class' can or can't make up welders pulling 55 hours a week on overtime and an accountant working 40 hours a week, then the distinction is arbitrary. That is why Marxist distinctions of class are superior. They are dictated instead by your relationship to your means of production, and how you acquired the rights to that relationship.