Except measuring G-forces acting on a helmet doesn't directly relate to the forces acting on the head within it.
If the helmet didn't decelerate any impulse to the head, the range of impacts that it could theoretically protect the wearer from would actually be quite narrow.
This is wonderful understatement: “If the g-forces between the helmet and the brain weren’t different, the helmet wasn’t a helmet at all!”
If English was like Italian there might be a specific word for a non g-force withstanding helmet and otherwise.
With the advent of plate armor, offensive techniques began to focus on concussive force in order to disable combatants, including war hammers and maces. A blow to the head with only a bit of steel between your skull and a mace would be a fatal experience without any padding. Even with padding it was notorious for deafening and disorienting knights, due to noise and (presumably) brain injury.
But for pure G forces, you’re right. A helmet with no padding is effectively similar to not having a helmet at all.
Your head is in a suspension within the helmet, much like your brain is in a suspension within the skull.
Your skull can accelerate at extremely high G's without harming the brain as long as it stays well within the modulus of the suspension. i.e. not for too long. The helmet adds another suspension on top of this.
For this reason, when studying head impact for football players, they mount the accelerometers in the mouth guard. This more accurately reflects the real g-forces, as the teeth (ideally) don't move much relative to the brain during an impact, and have the appropriate reference frame.
The differences can be extremely large. The peaks reflected in this graph are absolutely not real and should not be taken literally.
A low pass filter could easily be used to remove the impacts with the ice, but minus the impacts with the ice there's nothing in that acceleration trace that should be alarming for a professional athlete. The high frequency content is the concern here.
However, the real issue is not g-forces on _corners_ it is the g-forces on _head/helmet hitting the ice_ where 5 g from the first are rounding errors compared to 55g from the second.
I don't think I said they were, just that it's a worthwhile thing to measure to see if you should start finding a way to get better measurements. I agree they are not the same and this is not a definitive study. This is often how science works, you do something quick and easy. If it came out that it was only ever minor forces on the outside of the helmet, it's probably not worth investigating since the forces inside the helmet will be even less. If they're huge, repeated forces, it's probably worth trying to come up with a better rig to measure actual force and see if it's above a healthy level.