While you may dea with it every day, the statement of helmets do not provide protection is false!!!
The helmet takes the first line of abuse. If you shattered your helmet you likely shatter your skull if you’re not wearing it. The idea is that a helmet provides an initial protection, is it the do all end all of protection NO!, however without one, same fall same conditions you will definitely have worse injuries as your head is what absorbs the impact directly no cushion, no extra shell to protect what’s valuable inside.
As to other protections helmets provide or offer, they help how much who knows but some is better than none!
As to brain injuries, we know that if you don’t cause it any harm, likely none happen, we also know that if you completely destroy it, it definitely causes harm! Anything else in between is a guess as to the outcome.
So, helmets protect pure and simple. The only guarantee that they offer is that without one it would be a lot worse.
Protect the head, protect the brain, avoid the headache!
BTW I deal with my sons brain injury daily (19-1/2 years and counting) so I may know just as much as you, though not by choice, the only difference I’m not a licensed medical professional.