When it comes to stopping power, we’ve come a long way since then. The ECH/IHPS/NG-IHPS can stop a 17-grain steel fragment at >4000 feet per second. (Which comes pretty close to the velocity of similarly-sized fragments at the very point of munition detonation.) The best of the WWI helmets might stop that same fragment at a little bit over 1000 feet per second. So the modern helmet is a >10x better kinetic energy sink, at least against steel fragments.

(Against heavier lead handgun bullets, the picture is less clear. Steel helmets tend to over-perform, as they present a hard ricochet surface for soft lead bullets, and modern composite helmets don’t do a very good job of managing shell deformation, even against fairly low-energy handgun threats.)

Against blast waves, it’s true that there has been no significant improvement. Really, the only way to manage that problem would be to implement closed-face helmets, like motorcycle helmets, which is a deeply unpopular notion.