And the word "middle" in "middle class" is an elastic social concept because it is not tied to any precise formula, with no one really holding the authority to establish such a formula anyway. But even though elastic stretches, it can't be infinitely strectched without snapping and ceasing to be useful. At some point common sense has to be applied even without a precise formula. It just seemed to me that calling the top 2% part of "the middle class", even acknowledging all the variables you mentioned above, is too much of a stretch. It is true that people at the $250,000 a year income level in many ways have more in common with people making $50,000 a year than they do with people making $50,000,000 a year, but I would argue that's sort of like saying a dog has more in common with a cat than it does with a parrot, but it still is not a cat.
And in this case we are not having a theoretical abstract discussion, we are defining acceptable levels of imposed fiscal austerity based on a equally undefined concept of "shared sacrifice". Common sense has to be applied because real decisions must be made and standards are being defined in hard terms in Washington DC as we speak. You are absolutely correct that this discussion is about the upper boundary of a rather large interval, and in short my point is to agree with your observation that it's "Perhaps too large,"
It's being argued for policy purposes that people earning at the 98th percentile need a continuing tax break because, among other things, "the middle class has suffered enough". But their proposed tax break reduces federal revenues and thus increases by that same amount the funds that will need to be cut from budget items that millions of people far below the top 2% depend on. That type of reasoning fails the sniff test.