Re: minimum weight
"I guess you've never read or heard about the violence that happens once someone pulled the eject lever?"
I have, enough to know I'd never want to do it unless there's no other choice.
A substantial proportion of pilots who eject spend the rest of their careers flying desks thanks to spinal damage.
The fact that this is related to the mass of the helmet indicates that this is related to the compression forces generated on cervical vertebrae when the eject rocket fires. Ejector seats clamp the pilot's head to the seat back during eject specifically to ensure that forces are vertical and to prevent whiplash injuries when the chutes open.