>other factors like free time have worsened if compared with centuries ago.
This might be true if you consider being holed up with your family for the entirety of winter as "free time." Also, these studies always neglect the amount of random work that needed to be done before technology (e.g. fetching water from a well, chopping firewood, weaving baskets, etc).
Even ignoring time spent doing non-work things we don't do, free time has increased a lot over a century. We have good data on this. Factory shifts circa 1900 were long, and 2-day weekends rare.
Unless "centuries ago" means several centuries, in which case maybe it's murkier, the pre-industrial world was different. IIRC hours worked increased in the pre-industrial build-up to the revolution -- perhaps because there was more to buy, and people adjusted to try to buy things, rather than stopping when they had enough to eat.
This might be true if you consider being holed up with your family for the entirety of winter as "free time." Also, these studies always neglect the amount of random work that needed to be done before technology (e.g. fetching water from a well, chopping firewood, weaving baskets, etc).