On one hand, it seems like it would obviously have been miserable. So much more likely to lose your children, especially your infants, and death was more present in general. Medical care was lacking (nearly everyone was malnourished too), work was hard and constant, and there's a matter of social justice. First off, gender. There's a 50% chance you'll have 0 rights whatsoever. Even if you are a male, unless you're at the tippy top you are under worse impression than most realize, we complain nowadays that poor people can't afford nice things. If you were a peasant, you simply couldn't have nice things, doesn't even matter if you somehow get the cash. Best case scenario, 5% of the population has rights
However, they were very ignorant, and ignorance is bliss, right? They may have had some way of coping with the loss of babies, and of life in general. The average person was as religious as only wingnuts are today, heaven was a more real thing to them and their society reinforced that more. Opiate of the people, it helps them cope with loss. Perhaps they took more enjoyment in their work, or they thought it good for the soul, somehow found a way to deal with pre industrial farming even though it's probably a bitch to do. And unlike the average American today, they were never under the impression they ought to have rights to begin with.
Do any of you have any insight?
Instead of thinking about all of the things we have they don't, think of all of the things they had that the generations before them did not. That's exactly the way we think today and they way they did, too. A hundred years from now someone will wonder the same thing about us. How did we manage to deal with people dying from cancer? Driving ourselves everywhere with hour long commutes to work? Taking an eight hour plane trip? We may grumble about these things now, but they don't make us miserable.
While infant mortality was higher than today, it was most often improving with time. New medical advances were being made constantly and new inventions made life easier every day. Just think of how much society advanced when the printing press spread across the world. So much better than having to write every thing entirely by hand. Now every family can invest in a bible, or buy the yearly almanac to know how the weather will be this year or when the moon will be full and it's easy to travel at night. Or something as simple to us as a fireplace, channeling the smoke out of the building and reducing the risk of a house fire. Then add the flue in and you'll keep so much more of the heat inside, reducing the amount of fuel you need. Human history can be measured in the small and large inventions, advancements, and discoveries we make. The ones we make now are no more amazing or important than those before. And while we build on the foundation of what was discovered before, there are so many foundations we haven't even started yet. We don't feel sorry for ourselves for what hasn't happened yet, just glad that we've come this far and it was no different 100 or 1,000 years ago.
There are a lot of very general assumptions that need to be addressed here that just don't hold up.
First of all, the average person before "modernity" is an incredibly vague qualification.
How are you defining "modernity"? There isn't some sort of objective definition beyond "the present", which is both relative and has the problem of having an indefinite starting point. When does "modernity" start? Additionally, the idea of what constitutes "modernity" is very culturally and historically contingent. "Modernity" in AD1700 England is very different from modernity in 400BC Athens.
Secondly, there isn't one set of characteristics to describe the average person through all of human history, whatever your definition of "modernity". The situation of an average person in a society is very much contingent on the historical and cultural context of that society. You can compare subsistence practices to get a very general idea of what life would be like, but even then there is huge variation. There are some sedentary agricultural societies with very good health, some with very bad, and many with middling health. To generalize ("average") across all societies is very nearly impossible without restricting both your temporal and spatial ranges.
To elaborate on that, you are very much overstating how horrible life was in the past and perhaps ignoring a lot of the complications of "modernity". For instance, the statement that:
nearly everyone was malnourished too
Is really not defensible across the board. Surely there were many populations where malnourishment was a constant threat or a period part of life, but there is very good evidence for other societies were nutrition wasn't a dire affair on a daily or even yearly basis. I can think of several studies of archaeological populations that suggest fairly good health and nutrition on the basis of skeletal remains. I can think of others that find the opposite, but to generalize is not defensible.
Additionally, I think we have to address the significant downsides of "modernity", if by "modernity" you include the expansion of the capitalist world system and European colonialism, which I think should be included since the present - however strictly you define it - is very much a product of the global expansion of those systems.
For instance, we can talk about all the potential social and psychological issues posed by capitalism, urbanism, and colonialism. Just for a classic, see Marx and alienation. An issue not dealt with by pre-capitalist societies. When you say:
Perhaps they took more enjoyment in their work
That is basically Marx's argument about alienation. The satisfaction people in a pre-capitalist economy took at their job compared with the satisfaction of a factory worker.