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.
Yeah, there's no problem with a meritocracy as long as the top and the bottom of the gradient aren't (literally can't pay bills -> more money than you could ever spend.)
Like in no sane world would people willingly become surgeons for the same pay as a sanitation worker, that's just fucking stupid. Why spend a decade going through school to be a doctor when you could just go pick up trash and make the same money? We have to have some kind of variation in pay scale or society wouldnt function.
Like you said, how much difference between the top and the bottom definitely doesn't have to be what it is.
Yeah but in the current form of meritocracy both the surgeon and the sanitation worker are relatively poor compared to the upper class. And that exactly is the problem: you cant get rich just by working.