Personally I think it is obvious why the connection between stress and 'subsystems' is there. Stress puts the body into survival mode. Heavy breathing is an example. But when the stress holds on for too long it exhausts your body causing all kinds of trouble. The most extreme example is a burnout.
In the Netherlands it was estimated that a lockdown would save 150000 life years but would cost 650000. This takes into account a huge number of factors. For example health, but also job safety, happiness, and so on.
A lockdown causes stress for a lot of people. It seems you are not one of them.
I think because I'm not stressed about it I'm definitely in a position of privilege. There are people who could not work during lockdowns - and I can completely understand why such people would be stressed. Not being able to make a living, and not knowing what's to come.
I can't imagine life in the distant past being less stressful.
The modern world has the ability to stress you out over things you can do nothing about (or at least, not very directly and quickly), for long periods of time. Sit down and watch three hours a day for a week of whichever news channel pisses you off the most if you want to see. Some of you reading this already do that, so you may not even notice how pointlessly stressed that makes you because that's how you live. It also has a bunch of other humans who find it advantageous to stress you out that way and bend a lot of time and effort to the task of continually stressing you out, because they prefer that you not be able to carefully think about things but that you react less thoughtfully. You spend more money that way, among other effects.
Past life would spike the stress levels more often, sure, but it generally lacks the low-grade continual stress you can't do anything about. The exceptions that leap to mind (sieges! famine!) would generally be exactly that, exceptions. And in those cases... I'm sure the continual stress of sieges and famines wouldn't be good for them, either!
If your village is raided and you escape harm (quite the assumption), why would you generally return to "baseline"? What if the raiders took all your food and you can't feed your family? What if your family was murdered or raped? What if your village was destroyed and you're now a vagrant?
As I said, when constant persistent stress was occurring, I'm sure it wasn't any better for them than for us. But those were the exceptions. History writes about the famines and the sieges precisely because they're the interesting exceptions. Most people, most of the time, were not in a siege or a famine or under any particular threat from a neighbor.
Today, millions upon millions experience this mid-level persistent stress all the time, for decades. In the 21st century first world, it is the norm, rather than the exception. I don't think that's how it used to be. It especially didn't used to be that way when the danger of famine or siege is as low as it is now, making the stress response even more mal-adaptive.
It was a great summer, can confirm.
Hindsight is 20/20. Back then we didn't even know well how it transmitted, or the exact percent of deaths/long term effects if you got it.
However flawed or not the antivaxxer's reasoning, imagine the stress of having to choose between yours and your children's livelihood or being forced to inject a substance you consider risky into yours or your child's body.
It's more stressful to be sick two weeks and struggling to breathe because you got COVID, and I'm saying that as an asthmatic who is not scared of mild difficulty to breathe.
There is no sensible posture to rationalize antivaxing, but every country has a percent of the population who hesitates about vaccination, and a percent that not only refuses it, but stubbornly refuses to practice hygienic measures. This should be taken into account when designing future health programs.