I have to disagree on utility of carbon armor. That thing has plasma damage modifier of 50%, and that fact alone makes it worth the effort as plasma is most frequent and most dangerous damage type in late game.
Yes, but Chainmail already comes close to that with the (S) version having 60%, while NOT being vulnerable to the resulting secondary fire. This hardly matters, anyway. Even at 50%, from the front, a plasma rifle will still pen. This means you don't have adequate protection anyway and will still be using the standard methods.
Also, plasma is never the most dangerous damage type, it's always concussive. Only Plasma Scorchers even come close to the threat level posed by AI grenade cheats, as the AI doesn't have to pay TU costs for actually pulling a grenade out of his inventory and can use it with no hands.
Other advantage of carbon armor is that it has good night vision an thermal vision, has no TU penalties (i acutely avoid using power armor on my best gals as I hate TU penalties on anything I use for melee)
No +TU modifier *IS* a TU penalty.
and is simple to produce as it has only chemicals, life support and optronic parts as components
...and requires a printer, which is means you have to have fully established a printer base just to print second-string armor that only comes into being at the very end of its tier.
I use it as main armor type on my B team that i don't want to bother equipping with relay fancy and exotic armors. It is simply the best late game filler armor for cannon fodder and line grunts.
I use Blitz for that role because Carbon penalizes you 30 TUs by comparison, and is easily thwarted by a waist-high fence. It does not hurt that at late game, it USED to be the primary line armor, so it has already been produced in abundance and is now being partially phased out in favor of Assault and Annihilator (but never entirely, it's just that good).
On secondary troops who don't have maxed TU and medals that grant more TU, losing 30 TU effectively immobilizes you. You will eat so much more fire simply because you can't get back under cover, and Carbon can still be penned by the vast majority of enemy types...while Blitz has a shield, which means you can always freely absorb some of the most dangerous threats that can't be dodged, so you won't get penned by even a bazooka trying to exit the ship. And it, too, has decent NV and ThV.
It doesn't help that the primary threat profile of second-line troops is generally not plasma-based, since you don't send second-string units out to fight plasma.