The risk of not wearing a helmet is likelihood of something happening and the consequence if it does.
The paper is a sensible study of likelihood but I don’t think you can deduce from it that you shouldn’t wear a helmet as an individual.
Removing the fixation on helmets could reduce the likelihood of getting a bang on the head in your lifetime from 5 times to 2 times. But the helmet might prevent any serious consequence all 5 times.
I’ve never been hit by anything (touch wood) but have hit my head twice due to just falling off, no one else involved. Both times I split my helmet and got concussion. So in my case a more relaxed stance on helmets could have had severe consequences.
Others will have totally different experiences but if you are going to use stats to decide whether to wear a helmet you have to see the full picture.