People in this thread have already described how it's used as a semantic mechanism to obfuscate and mystify material reality. Reactionary politics of all forms (liberalism, monarchism, fascism) rely on dancing with signifiers to maintain hierarchies and prevent a critical mass of class consciousness from forming.

But strip away the illusion and there're still class complexities on a material level, one of the most important of which is the racialized and patriarchal class intersections, another being the dichotomy between developed/undeveloped nations. As Marxists we don't have any influence over the flow of culture and information, so we can't just brush over these material class differences in favor of working class interests, the way the bourgeois media can do so in favor of bourgeois interests.

We have to be strategic in where our finite efforts and resources are focused. That's why a nuanced class analysis has always been a key part of any successful revolutionary movement.

Interestingly, some of those who reject the middle class myth can fall into the same class reductionism as those who buy into it, which is a misguided, disproportionate focus on white male workers. The "true" subaltern in the US is likely composed of service workers, disenfranchised immigrants, and prisoners. In this sense the "true" middle class might be petty bourgeois, labor aristocratic, and professional managerial. Regardless, we shouldn't use such an empty signifier if we can avoid it.