It might provide more protection, at least against blunt impacts, but creating an interlocking hard carapace and then subsuming it into a padded over-vest strikes me as being both more expensive/difficult to manufacture and repair or replace and heavier and more wearying to wear than a simple rigid cuirass.
I suspect you'll probably disagree, given the bulk of your artwork, but I find rigid helmets over fabric or fabric-covered armour to be very visually disharmonious (likewise the reverse; bare metal armour with fabric-covered helmets like Hudson and Frost in Aliens), particularly when the level of armour coverage goes beyond a simple ballistic vest, as in the Warfighter iterations of Ghost Recon and Medal of Honour (though in those, both the Ghosts and the SFOD-D have fabric covers on their helmets so it doesn't look that bad).
If you've got a big, high-tech helmet that you're not going to put a fabric cover on, I think it just looks better if the metallic components of the body armour are also visible, like Boba Fett's Mandalorian battle-suit, or, perhaps more directly referential to your own work, the bottom-centre and bottom-left chaps here (this would have the additional advantage of saving the flak-vest segment of the armour from a lot of wear and tear by directly exposing the rigid plates to enemy fire, as well as aking the latter more easily accessed for replacement, though the question how exactly one might attach the same to the flak vest sufficiently solidly might pose a problem).
This is all just personal-preference stuff, though. Please don't take it as any sort of complaint against your work, which is absolutely brilliant.
well i never really liked cuirasses i suppose. i kinda took a hint from the modern russian army when it came to the whole carapace armor idea they're body armor is also made of multiple overlapping plates. they're reasoning being that if it gets hit.all you'll have to do is remove one of the many small plates in the vest, instead of removing one whole large plate. so it won't be until all plates are hit when you have to do some major repairs and replacements.
also it's due to the definition of carapace armor. warhammer's definition is that it's basically just heavier duty flak armor, made of ceramite, and armaplas, rather than plasteel, and flak boards. the real world's definition of carapace armor is that it's basically any type of armor composed of multiple overlapping plates. due to the fact that i decided to follow the real world definition all flak armor had to follow suit to fit with the aesthetics. which is why i base flak/carapace armor on real world body armors from all over the world.
now my personal definition of the difference between flak armor and carapace armor is that flak armor is composed of a soft ballistic vest with a single large plates inside while carapace armor is a soft ballistic vest with multiple overlapping plates inside.
this whole personal choice of aesthetic is probably due to me being a bit of a history/military buff, drawing 40k weapons and gear based off of real world stuff throughout modern history is pretty much my way of putting my knowledge to use in putting my own twist to my 40k works.
i find this cool, that some one cares just as much as me what type of armor the krieg (and similar units) are using! personally, it always felt like the solid cuirasses of the Krieg gave them slightly more protection, because as far as i can figure it, why would you build your armor to simply protect you from las-rounds, or stub rounds. (though i suppose if you put a Krieger against some guy with a bolt gun, it wouldn't be fair anyway because bolt rounds annihilate human organs from just their shock wave)
point is, everyone has a personal preference, and i must say...your depiction seems just more...familiar (probably the way the vest looks, i like that kind of stylish vest armor type stuff) excellent picture btw
It appears the Death Korps modernised to Wehrmact standards-still over 40,000 years out of date though
Seriously though, some extremely cool work as usual, the Kasrkin's armour looks more evenly spaced around then the big slabs of carapace they normally wear, it goes with the Cadian's professionalism theme-intelligently styled body armour instead of a almost Medieval design the models have.