Ah, I hadn't thought of that. I'd still think that the other helmets, given their general functionalities, would be suitable for such pressure. It doesn't explain the rest of the variant, though - why is there still so much flexible bodysuit exposed? Ideally, there shouldn't be any at all. Anyone wearing that is going to get crushed no matter how well their head is secured.
Also, a thing I forgot to point out - previous games' bodysuits, though exposed, have been hard material. It's all been sliding panels and stuff, not flexible fiber suits. Fiber suits are fine when shielding is involved, but it's nowhere near as practical as a hard casing that still allows movement when fire takes those shields down.
Of note: Dang I actually sort of like the soldier variant. It's still got a lot of bodysuit showing and I'm not a fan of the weird jaw shit going on, but it's nice and chunky looking. It's something you could actually reasonably deploy. Mark IV is nice too, since they kept it bulky.
Not-quite-EDIT: But they didn't have to be simplistic. If you recall some of the promo stuff for Reach, they were able to increase their polygon counts by a huge amount. If you compare the assault rifles between Reach and 3, it's obvious that Reach was much more detailed. The difference is that it was detailed in a realistic manner. Instead of adding slopes and curves to it, they gave it gun parts - a bolt, a canister of gas for pressurization(?), rivets, etc. Same with the armor, especially helmets - Reach added cameras, edges, vents, etc.
Compare:


They did not add any absurd mandibles (Raider, some others), inverted-Y visors (Hazop), Banshee Wings (Raider), or Unicorn horns (Fotus (also note: none of the helmets in previous games looked like Megatron from the recent Transformers movies))
It's possible to improve graphics without resorting to generic, overwrought greeble. I know it's the current trend in gaming, but it was a trend previously only exhibited by Halo's mediocre competition. I just think it's a shame that 343 was handed this historically beautiful series, looked at the tryhard knockoffs, and thought "Yes. We are going to imitate that."
Not-an-Edit-again: Yeah, thanks BTS, that's an important thing I forgot to mention earlier. I'd complain about this stuff if I'd seen it in concept sketches for an N64 game. I'm not complaining that they're high polygon, or even high detail - it's just that the designs blow.
Actual EDIT: Formal apology for cluttering this thread with my opinions. Wow this is a large post.
Another EDIT: Wait what's the point of not having visors. Spartans have specially enhanced eyesight, I'm sure it's more cost effective to just give them glass. It's not even a weak point, glass can be pretty tough and I'm sure the UNSC has access to more than plastic sheets.