Ahh, another trope of "it's modern so it's better" . . . Those appear to be around a 45 pound pull, a rather standard bow for modern sport archery. They problem is that most medieval war bows (for non horse riders) started at 80 pounds and went to 150 for english longbows. And for the china area, the Qing bow (about the size of those shown in the manga) used by the military from 1650-1730 an 80 pound bow was considered minimal for an adult man. Modern mass produced bows would be considered childrens playthings.
Either the author didn't do their research, or all his subjects are far too weak.