A 4' tungsten needle at high subsonic speed would be a scary thing. Maximum range of 5+ km, almost silent, and able to punch through meters of concrete. It's not quite an anti-tank weapon, but if it hit a car or a person it would just leave a hole and a thump. It'd go right through an engine block and bury itself into the ground so deeply that the hole would fill itself back.
I've also seen what a modern broadhead can do to a moose. Warning: this video is horrible.
https://youtu.be/3VhEYvHdVa0?si=vsK_aWdSxJ3ylYpU&t=70
That arrow goes right through the ribcage and shreds a lung. The animal coughs up a pint of blood immediately. In less than a minute it passes out from blood loss.
All to say... maybe we wouldn't kill people on the scale of a nuclear bomb. But if humans really tried to go to war with arrows, it would be awful. Guns are better at killing than they ever have been, but bows have also gotten better.