I think you're trying to draw too much of an analogy here. The point is just that advertising jQuery expertise on your resume today is evidence (though not especially strong evidence) that you might be someone whose skills are of diminishing relevance. Myself, I'm not convinced there's much harm in using jQuery, it's not exactly heavyweight. But if in fact fewer and fewer pages include it, then your expertise is relevant on fewer and fewer pages. It doesn't make sense to add a dependency on jQuery to satisfy a single dev's preference.

If your expertise is in low-level browser performance but you lack deep knowledge of React/etc, your skills aren't of diminishing relevance, and probably won't be for a long time.

IME, people list jQuery in their resumes all the time, typically as part of some previous job many eons ago. But I have read hundreds of resumes and just don't see people advertising jQuery as a primary skillset anymore, so to me suggesting that people still do this sounds very close to a strawman.

Something like Angular.js is a more apt example of a skill people still do advertise as a primary thing in their resumes these days and it most definitely plays into the diminishing relevance thing. On the other side of the spectrum, you have newbies writing down "HTML/CSS/Javascript" in their resume, which basically screams zero experience (aka "low/no relevance until they learn to speak the cool framework lingo"). There are plenty of other quote and quote "uncool" skills in actual resumes. Flux. Sagas. Ember. Etc.

So, yes, an argument can certainly be made that recruiters/interviewers do "discriminate" against various stereotypes to various degrees, and it isn't necessarily always based on ageism. A recruiter that reached out to me recently had an interesting term to describe this phenomenon: "skill commoditization", aka looking at people as snapshots in time, and evaluating some skillsets to be intrinsically worth less than others, even if they have some amount of overlap, instead of looking at people as malleable entities. It's worth thinking about how treating developers as commodities might hurt your hiring, especially if your hiring revolves heavily around evaluating for expertise in a specific framework.

I am not sure that the story has anything to do with the situation of jQuery today, because as I can see in your story there was a guy whose skills were of diminishing relevance, but surrounded by people whose skills in that area were never a thing in the first place, what I can draw from your story is that it's useless to cultivate an expertise in a niche field because it will be irrelevant in a few years?

I don't think you're really listening

Thank you. That needed said.