1) Why the assumption that X-Com uses this specific material you mentioned? I would have no idea.
Because aramid yarns of various types are already basis of majority of available protective vests, though usually they're the popular kevlar. Since I actually pay researchers big bucks to research adequate protection and, especially early game, one has to be concerned more with melee-wielding hooligans, wild animals etc then it makes only sense that some protection against slashing and puncture attacks is the priority and with various common armors against such kinds of attacks readily available, it feels like those scientists went extra mile just to leave such critical weakness in.
I wouldn't want armors excel at all types of melee defence but some late-game superscience hermetical armored suits having issues with some old slashy boys makes it look really weird, though maybe it's an issue of general scaling of defence vs attacks of simple melee weaponry, especially as the latter seems not to progress much technologically, even in hands of factions reliant on them.
2) Armoured vests have high armour values and no special weakness to blades, which already is good enough.
Glad to hear one armor is decent about it, I just don't see why many other, especially the fancy sci-fi ones shouldn't do well against some blades.
"Should"? But why?
Consistency, mostly. And progression, ideally - after all, big part of the game, be it mod or vanilla, is escalation and progress toward the realm of sci-fi and that in turn due to recognition that contemporary, yet alone ancient and relatively primitive weapons simply don't cut it anymore (I swear, the pun wasn't intentional).
I would understand an addition of a special anti-melee armour. Oh wait, that's the Bio-Exo.
Yup, there are armors which aren't bad against such things. I just ask to have a look at other armors stats as well so none, especially of the actually armored, later game variety will feel weak against regular, bogstandard knives. And while I think of it, adding a mention or two to some armors which don't have such yet of how they do good against, say, plasma weaponry but are pretty brittle and so not good against low-surface kinetic weapons such as stabbing blades could be pretty nice flavor addition too.
AHAHAHAHAHAHAHHA!
Sorry, can't comment further
Come on, you know he probably meant open-field warfare against armored enemies