Perhaps that's indicative not of a problem with the measure but rather of a) a disconnect between our society's self-perception and its reality and/or b) a problem with our economic system, the opportunities available in it, and the saving/spending norms it propagates?
One interesting factoid I know is that 50% of Americans represent 2% of the income in America.
“The shrinking middle class” is a phrase that is part of common discourse here for a reason - I wouldn’t be surprised if 80% of Americans fit the parent comment’s definition.
The only one which is not a routine part of the middle class experience these days is eating strictly junk food because you can't afford anything better.
Every other part of that entire list is, sadly enough, "normal middle class" in the US.