I believe the fears about connecting a production computer to the internet are somewhat unfounded. Granted, Windows 10's update process could lead to some issues every year when the big update happens, and occasionally if a security update causes a problem, but most of the problems that you read about with these updates involve systems which are running very specific network configurations or custom business software.
Rolling release OSs (doesn't matter what the brand is and Win 10 is a rolling release) are not good for a production environment. With big updates twice a year and really not a good bug testing protocol, updates causing issues for those happy few users are bound to happen.
My dad has had an issue with Win 10 on every friggin' major update release and he doesn't run anywhere near the niche software that we do. His only point of contention would be is that he does go for the more bleeding edge components (ones that forums are still a couple of months out on tips and hints on how to set things up and troubleshooting). Windows also doesn't have a very good track record with updates/upgrades over the years (I've been using Windows since the DOS days when I was a little kid up to 8.1 (on my own computers), still run Win 98, Vista, 7 and 8.1 in VMs for nostalgia) and that's actually to be expected with the copious amount of hardware/software combinations. It's hard for them to get it right. Even Apple doesn't always get it right (release of High Sierra and the root login issue comes to mind) and I have far less sympathy for them due to the locked down nature of that hardware/software.
Security updates should not be a problem in updating. Where updating gets to be a problem is when you have features being implemented or removed. Some program that you may be using that depends on an older API, no longer works because the newer API doesn't support it (or vice versa). That's on MS' schedule, not yours on when that happens. And I don't know of a way to keep new feature release/removal from happening without using 3rd party scripts (which has it's own security concerns).
If Win 10 allowed for only setting up security updates and nothing else, I would be that much closer to still being on a Windows rig, between that and the telemetry (I know some people could care less about the privacy aspect of it (right or wrong), but compiling and deploying said telemetry does affect computer performance (it's doing a lot of it), as it doesn't always do it during the down time either) are what have made me jump ship from Windows.
Here is the biggest problem with Windows updates, the users are still at the mercy of MS actually fixing an issue if they do fix the issue (and on their schedule). Look at how long the last major update took for them to get right. Since we are talking about NASs, wasn't there also an issue with some users not being able to access their network shares? If that happened to me, that would be a show stopper until MS got it fixed. The more involved the setup, the more the worry.
As to if the concern about production rigs is unfounded or not. How many threads have been on here where users have done an update and something no longer worked? Be it a Win update or a software update? Sometimes a user was able to fix it on their own by rolling back, sometimes they had to wait for a fix.
To me, it's not so much if it's unfounded (as there are real issues that have happened out there), but how risk adverse are "you" and how much of a risk do "you" believe that there is for it to happen on "your" setup.
The big problem with being on the internet is what the computer user is doing on the internet, i.e. email, browsing, social media, as entry points for malware and viruses and phishing scams. That requires discipline on the part of the user, as well as not automatically doing every update that comes along willy-nilly.
This is a huge part right here. The human component is the biggest, the biggest thing. Unfortunately, with regard to updates, sometimes those are forced on a user. I no longer know of a way of disabling Win 10 updates as all of those avenues have eventually been plugged up by MS. That leaves 3rd party means (scripts etc). Not so much on trusting those.
And even though I moved to Windows 10 pretty much as soon as it was available, I have experienced no issues from the updates that come in regularly.
People's experience will vary of course. I only have to deal with one Win 10 computer and that has been a pain in my butt since 2015 (components have changed over those years).
That said, your best safeguard against rogue updates is daily automatic backups which can be used to bare-metal restore your system.
Proper backups would mitigate a lot of the issues that people deal with. Updates, malware/ransomware etc wouldn't be a thing if people just did proper backups.
It doesn't always help on how Windows handles permissions as well. Making things easier for the end user comes with some sacrifices.
Of course, not having those production sensitive rigs with internet access would preclude all that as well.
