That's a good point. It is not only resistant to splashes (IP 64) you can hose this down without any effect (IP65), we conduct our own tests using this method. Of course if you blast a high pressure hose from the side (IP66) or totally submerge it in a tank of water (IP67) then of course there will be some leaks. To design the product to IP 66 or 67 ratings would make the product prohibitively expensive for the general market and is not necessary for the purpose this product will be used.
IP64 is not bad water resistance, and it's easy to first add hardware wallets inside of zip bag to make it more waterproof.
And some hardware wallets have waterproof protection already (satochip, tangem, coolwallet cards, ngrave, etc.)
You're saying that the hardware wallet's case can resist hacking signals. But what kind of transmission are we talking about here? Does this mean *any* sort of wireless signal? Because a hardware wallet is not supposed to be having any in the first place, and you can do firmware updates over USB if that is necessary.
I don't think faraday bags are much needed for airgapped wallets like Passport, since they only connect with other devices via camera, but they could offer protection against EMF pulse attacks that can fry any electronic devices.
Faraday bags are also perfect to be used for credit cards and car keys, they are proven to protect against modern thieves who are using antennas to catch a signal from keys and open your car.