Obviously the Swartelves can block magic based interference at some level otherwise Harry would be living in a cave.
I'm not saying
no shielding is possible, but that
existing mundane shielding on military technology
designed for EMPs shouldn't do anything vs. hexing.
The Svartalves are designing specifically to deal with hexing, already understanding the principles of magic, and likely using magic themselves.
So exactly what is the downside of nuking the Fomor who don't have a magic helmet assuming that they murder Chicago?
Well, if they had already succeeded in killing off Chicago,
then using nukes might be considered.
But it still wouldn't accomplish much... Harry says that Ethniu with the Eye of Balor is the big problem, not the Fomor army.
Without Ethniu and the Eye of Balor (and its super-hex effect) a Fomor army could be dealt with perfectly well by conventional weapons. The powerful sorcerers like Mag from Even Hand can shield effectively, but they only have so much energy, and most of their forces would be minions who can't do that.
Morgan used a nuke on a Skin Walker. And that was crude compared to a modern device.
A skinwalker isn't
remotely on Ethniu's level. Listens-to-Wind was able to chase one off; Ethniu is significantly stronger than Mab, therefore much more than a match for
the entire White Council.
Which of course is not what Jim is going to write.
Sure, nukes won't show up in BG, but re: mortals vs supernatural world in general, I do think it's important that mortal weapons work great against wizards and vampires and stuff (e.g. sniper rifle vs Harry in Changes), but that there is an "upper limit".
Mortals can't really invade the NN without wizards helping, and anyway reality is mutable there at the will of the ruling powers (like the time bending in PG).
And Ethniu could probably literally just ignore being hit with any mundane weapon. It would take something like the Swords or the Athame/Spearhead, or maybe mordite, to harm her (short of a comparably powerful being, like Hades or maybe Ferrovax).