Back in the 1970s, when everything was subjective and hence ill-defined, while it had no credibility among those qualified in electronics I'd just laugh at them, and buy the next issue. But nowadays, when their nonsense is so much more quantifiable as nonsense, I begin to despair.
I agree, although with analogue signals, and particularly with below-spec cables, there is an improvement to be had from using at-spec or (maybe) above-spec cables.
Early days of digital TV, I had a digibox connected to an analogue TV with a Scart cable.
The original Scart cable, as supplied, was a bit thin, probably didn't have individual screening between signals. Quality was poor, shadowing on picture, occasional interference.
Replaced with a fatter (but not premium priced) Scart cable that had individual screening (between video and audio signals, for example). Interference went away.
I then wired my own Scart cable with 75 or 50 Ohm (actually can't remember the required spec, but I followed it at the time) cables for video and appropriate for audio. I got a noticeable improvement in video quality and sharpness.
Wanting to go one further, I then bought some "oxygen free" cables etc, getting obsessive about it all. Made up a new cable with the much more expensive wires. No difference.
My conclusion from all this - once you're at spec, you're not going to make it any better.
Ian