Earlier quoted context omitted.
You shouldn't be down voted. Context matters an incredible amount in the English language. Plus, the US doesn't really have classes the way the OP is concerned "middle class" will be interpreted. I'd be surprised if anyone misses the point of this analysis either way.
As Wittgenstein might put it, there are two language games at play here. The first one takes 'class' as defined in the (legitimate) Marxist way, used to represent the relationship to the means of production (Edit: we don't produce all that much anymore, making that definition harder to parse). The second takes it to be specifically defined as a range of income distribution. That second one is what most people typical…
If by "we" you mean the US, this is not true. US manufacturing production was as high in 2015 as any prior year. Production took a big hit in the "great recession", it may be on the decline as percent of the total economy or as a percent of global production, but it's still a huge amount. https://research.stlouisfed.org/fred2/series/OUTMS