Panzer, your numbers look miss-typed you must have some decimal points in the wrong place.

Even a blunt javalin is more effective than an arrow.

Eduorius: I believe it has to do with a number of things:

Training: As someone who has lugged a modern soldiers fighting kit around on a hot summer day all I can say is eventually you get used to it.

Insulation: After a certain point all that felt and blocks in the incoming heat, at which point all you have to worry about is your own body heat, which will build up.

They didn't: Kats only really need one charge, they probably had their helmets off until they were actually fighting, rather like the old Corinthian Hoplites.