So ...
Let us assume for a moment that, these these things were battle accoutrements purposely made for assaulting (climbing) fortification walls; to protect you from whatever is dropped from above ... stones, boiling oil and the like.
The eye slits would be dispensable; you wouldn't wish to look up while climbing your ladder and risk having your eyes burnt by the oil ... or perforated by an arrow.
A wider brim would make too heavy; the shoulders would be protected by its own reinforcement
