Then you’re still at the mercy of the TTY application being secure. Having to go through the analog hole makes it much more difficult.

As for patching, you would ensure a secure root of trust and only allow read-only media to deliver said updates as another sibling points out

Air gapping is still valuable but it’s still hard to impossible. For example, stuxnet was delivered by an insider. So good physical security and monitoring is also needed to prevent against insider threats.

I think of the sensitive, air-gapped information as an infection. If an old and “infected” machine needs upgrading then it’s easier to put a new, freshly upgraded machine into the infected area, copy the sensitive data over to the new machine, then incinerate the old one.

Anything that does come out of the infected area in-tact has to be cleaned or inspected carefully to ensure it is free of the “sensitive data” infection.

That would happen in a secure environment with auditors and multiple sysadmins who would have the ability to do things normally disallowed. Different threat model

Assuming the goal of the air gap is to prevent information getting out. Stuxnet was not about exfiltrating any data, just causing havoc.

"Patching" is the fundamental reason airgapping isn't a sound solution, IMO. If you're a TLA you can probably find some secure, verifiable, write-only way to transfer patches to your air gapped machines. But for any normal person/organization; you'll very likely end up less secure due to how hard this is.

You can use DVD-Rs to load a WSUS server for Windows or a package mirror for Linux, I’d just be surprised if many airgapped operators were keeping on top of this.

This exactly how its done in many high security gapped environments. Once you get in a rhythm its not hard.