It's the 110 that's the problem, since that means at least 70 or so gets through in most cases and unless you're fairly high-level you don't have the HP reserve to tank that for long. Fortunately said Mantises don't have much in the way of DT or HP themselves, but extrapolate that to Veteran Legionaries with Ballistic Fists and you see why I'm concerned.
AFAIK there is only one pair of Giant Zion Mantis, they are more or less 'Legendary' creatures, so they should be VERY dangerous. Veteran Legionaries with Ballistic Fists ain't more dangerous than Veteran Rangers with Brush Gun, I don't really see the concern.
I don't mind opponents being able to get through the armor, but I am a bit concerned that the continued use of top-end weaponry to increase the challenge factor for L40+ characters will make attempting to stack DT impractical because you're not stopping enough of the damage as compared to the opportunity cost of amassing that much DT.
I would agree there isn't enough Tier 4 (as Josh put it) weapons on NPC. Tier 4 does about 40 to 60 damage, the increase of such opponent would make PA more practical along with better DT.