My first thought is, this is a study. Wait five minutes and there will be another one refuting it. Studies are like busses. If you miss one another one will be along in about 45 minutes.
Today, I can watch a 40's or 50's film and understand every word. Anything made after 1980 is iffy and anything made in the 3rd millenium is total greek.
However, with closed captioning, no problem!
My hoh friends all say after a few days they don't even notice that the cc is there. They actually hear the words because the brain inserts the extra info necessary to sort out the mumbles and funny accents.
Of course, all of us are NOT products of the leftwing school system. We all got out before the left took over.