I don't know where you're getting that notion. The overwhelming majority of people were agricultural workers and would work pretty much from sunrise to sunset. In the winter this meant shorter hours and more sleep (nobody stayed up late browsing the internet, for instance), but they routinely worked long weeks with only Sunday as a day of rest. True, their were other holidays throughout the year, but people didn't have nearly the amount of leisure time we in the West enjoy today. Producing food using nothing but human and beast labor and without modern fertilizers was very hard. They certainly worked at a slower pace than many of us do today, but they had to put in a lot of hours just to get by (and death by starvation--or at least death because you had been weakened by undernourishment--was not at all unheard of).
I understand your complaint, but I believe the lack of the metric system is strength. In fact, I think the designers of 5e went too far trying to make systems more rational (the decimal monetary system, for instance). The medieval world (I know--D&D isn't historical medieval, but it was always supposed to be medieval fantasy) was full of irrational systems of measurement. Traveling from one kingdom to the next might mean you would have to learn a whole new system of weights and measures. The quirkiness of the English system is only a taste of the confusion of the medieval world's systems of measure.
A quick Google search shows that while it's debated, we probably put in more hours at work than our ancestors did.
That if you can get your AC high enough that someone needs a natural 20 to hit, they either crit you or miss. Bugs the hell out of me.
