My (admittedly limited) understanding of baseband demodulation started with the swling I did as a teenager.
With that in mind, preserving communications would seem to be near the top of the list (perhaps just below clean water?) when things go wrong. Radio seems like a good backup -- perhaps even ideal.
So I don't think we should compare radio to just any obsolete tech out there.
An interesting (programming) talk by Jonathan Blow on the subject of losing knowledge! https://www.youtube.com/watch?v=pW-SOdj4Kkk
I get where you're going but concerning the abacus, I respectfully disagree.
I'm guessing you haven't seen the way some young Asian kids start using a Japanese abacus (Soroban), and after a few years have built a mental model of it enabling them to perform mental calculations -- faster than with a calculator.
Most of the good videos on YouTube seem to have disappeared, but some short snippets remain.
I wept for the state of public education, basic addition is lost skill it seems
What does this have to do with "public education"?
They could have been taught it in elementary school, but if they were in their mid-20s, then it would probably have been over a decade since they were tested on it even in secondary/high school.
And that skill would have atrophied with non-use on a day-to-day basis.
The evidence you provided suggests otherwise. :)
I'm sure the person can still add, but it's a bit slow(er) without practice, they got frustrated, and so handed back the change.
The potential costs are limitless (both in money and in lifetime because you can never be too prepared), the potential benefit is absolute, the risk (when assessing by statistical impact on total human lifes so far) very low. How do you possibly weigh such things?
While having the skill is a 1 or a 0 (either you know how to use a radio with some proficiency or you do not) the use cases for older/simpler technology get fewer and fewer gradually.
At which point can a system no longer afford to support technique x? Of course, it depends on the system but you are probably not going to wait before the probability hits 0 if you care even slightly about being efficient – but it's never an easy call to make.