Agreed. I say this after many many hours making my own cables with all kinds of materials over the years. I can understand the skepticism as it took a while before I even heard the word dielectric, but if you compare enough, you will start to notice a pattern.
I used all kinds of teflon wires for a long time because lots of people were saying that's the best and yeah I found it was an improvement over PVC and slightly over PE. Then I finally got into the cotton as dielectric and even bare wire and that's when I noticed teflon's impact on the sound. Teflon adds a top end tizz and brightness that isn't quite natural IMO. Of course so much depends on synergy and comparisons to suss out the distinct signature. Once I got into cotton, even the 'cheaper' 4N quality Jupiter copper (as opposed to OCC/PCOCC, 6N etc.) sounded great compared to the pricey teflon. Way more fluid and natural and clear. I haven't gone back to teflon since.
As for silver plated/silver I wouldn't touch it with a ten foot pole. Silver is one of those materials that makes me wonder just how differently *do* people hear music because I HATE the sound of silver - especially silver plated. It is such a totally different presentation from copper that I simply cannot fathom anyone not being able to tell the difference. Silver is almost always bright, bright, bright. Yes, there's a kind of exciting clarity in the mids, albeit kind of flat, that sucks you in for a second but the second those cymbals crash oh man yikes. Yes some silver wire is better than others, but ultimately the overall signature is the same. There is a reason why a lot of tube folks have silver in their setup.
As for silver plated copper, I've found that to be the worst of both worlds - the plating tends to be poorer quality silver making the mids to highs even harsher while the copper, usually also poorer quality, just adds a fuzzy haze in the lower registers. Now I'm sure there are exceptions, I mean there are a billion cables out there, but by and large this has been my experience as a diy'er.