> Modern European pilgrims on the Camino de Santiago seem to do about 20 km/day [1] and it's considered tiring but accessible by average people, not serious hikers.

Yeah, because they sit in the Albergue half of the day. You need to start looking for one around 4pm or it will be full because people tend to stop walking around that time. It’s also an activity that mainly retired people do.

You can easily do 40 km/day on the Camino routes with manageable elevation (the coastal ones).

You’re right about the equipment weight though, I can’t imagine what a Roman soldiers full pack must have weighed with the textiles of the time. On the Camino, you don’t really need to bring anything except some clothes.

I see the point with the camp but on the other hand after the third day you’re more limited by your feet, not the time, so you would still have enough time for that in my estimation.