I doubt there are sources that say it's BS... I certainly don't think it is BS, it is what it is. As I said before EMP pulses are naturally occuring and can be created, the limits are well understood. Shielding for the protection from them is well understood.
For power lines there are millions of fuses which will blow if the automatic reclosers are not fast enough to open connections all through the grid.
You mentioned a nuclear generated pulse blowing the filimates of street lights in 1962. Fimiliants blowing in old street lights with the way they were wired in series to avoid using a transformer, and were not metered loads, back then was common when there were lighting storms as well. That method of wiring street lights is 60 years out of date. More to the point street lights with filaments have not been much used during my entire lifetime.
The last thing you said about treaty and goodwill (and baloney) is as good as it gets. Nothing superior to that has ever been figured out.
If Russia were to explode several pulse explosions in the upper atmosphere as you are suggesting they could get away with it. I would expect Russia would not get away with it. They would be very sorry they pull that stunt.
It's not the damage if any from a pulse that would cause that firm reaction from US. It's our deterrence policy which would demand a strong reaction. If they use even one of them, we unload our whole wad on them. That's in the rules of this game.
I would imagine that what you are suggesting would draw a response where we'd go after every their entire nuclear force at land and at sea. We'd blow up their missile silos with small nuclear warheads, and we'd sink their missle subs were ever we found them. And I would think we'd find all of those missle subs. I think we've been able to track them with satellite imagery beneath the surface for years.