....to be fair, the cuirassier, provided it is thick enough (and it needn't be that thick, mind you) is conceptually good against blast, shrapnel and glancing blows as is the sallet helmet.

Remember that in WW1 Stahlhelm of the Germans was based on the their medieval knight armour.

(the English took the medival archer's helmet and adapted it while the French basically made a military version of a then modern day firefighter's helmet)

Modern helmet technologie makes them mostly lighter and more comfortable to wear in comparison to the WW1 or WW2 steel helmets, not necessarily that much safer.