They don’t call Germans “squareheads” for nothing. Most WWI or WWII German helmets I’ve seen seem quite small.
That dented pickelhaube was made of leather & the M1916 `stahlhelm’ partially solved the problem.
It’s steel with leather straps inside and the metal spike on top. I used to wear it when I was a child 30 some years ago while playing in grandma and grandpa’s attic. It would fall off my head if I put it on today as it would just be sitting on top of my head and my head isn’t especially large. I can’t imagine that this helmet was worn by an adult man.