The camera industry remains larger than it was in, say, the 1970s, by I think quite a bit. I looked the numbers up a while back, let me see if I can find them. Yep, here it is. In the 1970s, Polaroid is shipping something like 5M units/year, Japan is shipping something like 2.5M SLRs per year. All up the whole damn thing is maybe 10M units a year? 15M? In 2018 we're seeing 1.4M units a MONTH from CIPA, which doesn't include phones and also leaves out a handful of smaller sectors (MF, I think? Maybe all the European manufacturers? Film cameras, and probably a bunch of other little niches.)
Margins may be a lower, due to the vastly increased complexity of cameras, I don't know offhand. The contraction is not really from 20th century numbers, but rather from the massive explosion of growth in the early 2000s brought on by the transition to digital.
What is not clear to me is how large a company must be to successfully make a business out of digital cameras in this century. You could run a surprisingly small shop building the cameras of the 1970s, in the 1970s, and be successful by the standards or the 1970s. It's not the 1970s any more.