Yes thats true, but in the context of a cash strapped Britain, not wanting to spend much on defence, dont you think retaining the old Brodie Helmet (which in australia we just referred to as "the tin hat") was justified. Its a bit like the Lee Enfield. in retrospect, like the Mauser, there were better options available, but it just didnt make any sense from a cost pov to go to the trouble and expense to make that huge change. Spending limited defence dollars on upgrading artillery, or improving tanks, or the like, made far better finacial sense given that the old Infantry weapons were perfectly serviceable.
Statistically personal side arms account fopr less than 5% of enemy casualties in a full on battle. Artillery is about 50% of casualties, Tanks are about 5%, mortars and light artillery about 10%, air support anbout 5%, MGs about 15%, and things like mines, snipers etc the rest. Spending money on personal side arms, when all the combatants had bigger holes to fill, makes no sense. You make do with what you can.
Things are completely different now. We are in the age of the "small wars, and here, personal kit has more impportance.
As far as helmets are concerned, Ive got no data but I expect when the US redesigned their helmets they based it on some kind of data. Iremember reading in one of those defence journals that weight was a more significant concern than levels of protection. Arent the new US Hellmets made out of carbon fibre or kevlar or something?