That is only true in the sense that your Python 2.x experience didn't translate into your Python 3.x experience. That is, I think the overlap is similar on a language level. The difference lies in the libs/frameworks.
For the purpose of this discussion — carrying learned knowledge forward — it was minor.
Even jQuery is still helpful if you think of how it's accessing the DOM rather than just a set of magic functions to make things happen.
If you know Javascript you can learn Angular or React or Vue fairly quickly.
Obsolete does not mean you cannot use your knowledge anymore. It means that community are shifting interested into new thing, maybe for better or for worse.
In this case, I do not think stick with JQuery or old framework for 5 years is productive for programming. If that happen to any community I would say that is a downside, not an upside.
Except for that fact that community and newly graduated junior developer are ahead of me in something. I can live with that