Relying on studies data from 100+ years ago is shaky at best for a topic that requires much more precise measurements. The study directly links reaction times to IQ and creates a direct link between a decrease in reaction times and a proportional decrease in IQ. As others have said, this only works if the you wrap all or most of IQ into reaction times alone, subsequent studies have all shown increases in IQ in most places across time as the IQ test has become more wide spread and standardized to account for cultural biases (the Flynn effect). This also doesn't hold as reaction times can be increased immensely with training or decrease with disuse, reaction times also tend to drop precipitously in older people, this does not correlate to a similar drop in IQ.
What most people don't realize is that IQ is not always intrinsically linked to the biological capacity for intelligence, as someone said above me, just a change in environment can create a 20 point swing up or down and on an IQ scale 20 points can swing you from the lower end of below average right into the average range, or even the upper end of average into the exceptional range. IQ is a tool that is useful for a foundation, trying to treat it as an absolute indicator of intelligence is useless as the test is too imprecise to gauge a persons natural biological limits for learning and adapting to changing situations.
Historically education and study have also changed immensely since those times, The older studies this one uses come from a time where the only people they were collecting data on were other rich, educated, white, western men. So the Victorian era studies have a limited sample size that only tests a narrow range of people, the data is then extrapolated out with other studies that include women and other nationalities and ethnic groups. It's the same with education in general, the vast majority of educated people in the West over 100 years ago were wealthy white male landowners, we now live in a society where it is almost mandatory to at least receive a high school diploma or GED, this has a much much larger effect on our data pools studies that once only accounted for the top 1% are now including data from a wide range of people that were never studied in the past.
Another point, please stop treating the term, "peer review" as equivalent to, "the scientific community agrees with the conclusions of this study", it's intellectually dishonest. Peer review generally means that it has been reviewed by other people in the same field of study to find flaws in the methodology of the study or examine it for blatant falsehoods. Plenty of peer reviewed articles make it to publication every year that are summarily dismissed by the scientific community. Even the peer review panel itself doesn't have to agree with the conclusions of a study in order to approve it for publication. The study itself is a foundation, it is too broad and it's conclusions too vague to be anything other than a potential base for future research, studies do this all the time, they draw a simple correlation like showing decreasing reaction times in history or showing a link to high CO2 levels with the last ice age, and then lead their conclusion into a grand potential territory meant to spur further research into that area by saying things like ,"and this means IQ has been dropping" or ,"and this means we could be entering a new ice age". As with the ice age example future studies showed that, no, there wasn't another ice age incoming, and future studies in this area will probably fall into something like, "we need further research on how to specify reaction times with IQ measurement", or "Victorian and early 20th century study samples are too narrow, this justifies a standardized long term study with a diverse sample size".
As for your assertions on the quality of media, others have already told you that nobody remembers the crap, but let me tell you a story of my own. I have recently been cleaning out the room of my recently deceased great grandmother and found a box full of old books from the early 1900's. Pretty much none of these books were written by any author I'd ever heard of, they were all short story collections or short novellas, that I later found out were referred to as penny dreadfuls. And they were just that, dreadful, these were the early 1900's equivalent to the brainless dreck we see on T.V. today, stories full of 2 dimensional characters, plot holes, mindless action, and pointless sex (also lots and lots of blatant racism). Why are none of those stories or authors read much today? For the same reason nobody really remembers the sitcoms of the 90's beyond the gems that stood the test of time, (Stuff like seinfeld, and the Simpsons). Here's another one for you, Casablanca is often seen by movie critics as one of the icons of cinema, but it was part of a bulk deal by the movie studio that made something like 30+ other movies that same year, yet we remember none of those other 30 movies the same way we do Casablanca. That's because the vast majority of them tanked, movie studios back then released tons of movies on shoestring budgets with interchangeable plotlines designed to try and hit as many cliches as they could, remember this is before the widespread advent of TV, so Americans were flooded with new movies every week, only a tiny tiny fraction of which anybody remembers today.
Another point is that even the people we thought of as iconic masters of their era often went unappreciated, and even died broke and unknown until their music or art was picked up after their death by a later generation. There will likely be artists alive today who are barely known, who will be looked back on in 100 years as iconic or emblematic of this day and age, remember hindsight is always 20/20, it's far easier to look back and see what worked then, than it is to guess at what works now.
