why OHK knives are fine

You never run out of knife.

If 25 people can't tell someone is not on their team and they all get slaughtered by someone standing right besides them.....

They all deserved to die and hopefully they learned something from the massacre.

You also have a several meter kill area for C4. I highly doubt sprees are going to last longer than 5 or so people against competent enemies.

You also can knife faster then you can deploy and ignite C4. You're nit picking what is going to start happening. Nobody is going to care about C4 vs knifing, it's just going to be yet another thing you have to gun down four allies to get that one guy situation.

Having a melee weapon able to OHK someone is indeed fine.

"Balanced" does not mean that everyone to have the same TTK. It means that results yield are proportional to the difficulty to hit.
Shotguns are already able to OHK someone, and they are fine, because the difficulty to land a good hit with a shotgun is much higher than with an AR. So they can have lower TTK because of it.
The same can be said with melee weapons: As a stalker, who is the class who is the most advantaged theoricaly to get at melee range, I can say how hard it is to approach a target at such distance that you hit it with such weapon. So yes, they could OHK without being unbalanced.

HOWEVER:

1- OHK on the quick-knife is a no go.

You cannot give people melee weapons that yeld the same results than such a primary weapon without making it a primary weapon also.
Making the free quick-knife OHK is a no-go, because it would say that everyoen get something on par with a shotgun (shorter range yes, but greater damage...)
If you must give a OHK melee weapon, it must be something like a "Plasma Sword", a concept that is derived from RL Plasma Cutting concept, and used in many futuristics games, like, under, the Plasma Sword from Warframe:


2- Ammunition is to be considered
Melee weapons can have ammunition. Especialy in the future, where they must be able to go through things like energy shields and thus, use technology that would requier energy too.
A plasma blade needs energy. Without it, it is just a very expensive club-like weapon.
It is important to wonder what is more balanced: with or without ammunition

3- Should Stalkers be able to use something like this?
The most demanding people of OHK melee weapons are Stalkers.
It is not power issue: we kill people who are not on guard against us fine enough at short range with a simple pistol. This is a matter of how we would like to play. We are infiltrators, we would enjoy to be able to sneak in the back of someone to backstab them, but the knife is just not good enough to justify the risk to get closer than the distance where our pistols kill in 2 headshots.
Alas, there is a bunch of infiltrators-hater around, that already would make us disapear from the game if they could. Some players feel it would be better to be "safe" if they stand unaware in a spot that have been "secured".... and they are not, because we can be anywhere, so some time when they drop their guard, they meet a swift death from shadows. Those people think we are "overpowered" without a close look to real results, just because we piss them off.
So I can foresee what those people would tell if we were given such weapons... a river of tears.

I'm not an expert but I think you might be surprised.
Because as far as I know you might have a better chance to kill somebody wearing kevlar with a crossbow than with a bullet.
I think its something about kevlar stopping pointy but basically blunt bullets, but getting cut through by anything with an edge.
....
Basically (except, of course, if what I remember is BS) even today a knife might work better against body armor than a pistol.

I do assume though, that the knife would have to hit at an almost perfect angle to actually deal damage, and of course when you don't have a run-of-the-mill pistol and use a sniperrifle or something similarly high powered it will be better than the knife by virtue of having a lot more energy behind the attack. So, yeah, generally speaking a knife is not a good choice (in a firefight)

And leaving the topic of knifes vs bodyarmor - who the **** would attack the damned breastplate? Go for the throat or the armpit - those cannot be heavily armored or the guy couldn't even move/move his head anymore. (Even Batman wanted to move his head)

Sure, except:
1) Kevlar can be fortified with cut-resistant materials like Aramid which greatly reduce the cutting power of a crossbow bolt or knife.
2) Generally only police forces or personnel not meant for actual combat are issued Kevlar or "soft" body armor... the ceramic "hard" body armors that are employed by today's militaries are as crossbow-resistant as they are bullet-resistant. Knives would do nothing.

Please go try this on the PTS before you form any other opinions on OHK knives. This really does apply to everyone who has not actually taken the time to try it out on PTS VR targets and/or arrange a fight.

Let me reiterate something very important from my playtesting, The guy with the gun is going to kill the guy with the knife 9/10 times. OHK weapons are going to be a non-issue, the worst that happens is people start running around with their knife out more often because they are going for knife auraxiums. That's it. Clueless players are going to still get killed, knife or not.

True enough - my point wasn't actually that you should pick up your longbow to fight a war but simply that "modern" "state-of-the-art" doesn't mean all-around better and resistant to more .... traditional means of attack.

Regarding knife attacks I stand by the point I made in the last two lines: If you're that close you're going to attack a weakspot. There won't be hard armorplates at your throat or neck unless you're a MAX.

Although reading some of the descriptions you should be able to carve up tanks with them...
Also: Am I the only guy thinking that it would be hilarious to slash a sunderers/harassers tires and watch it go out of control?

I'm not sure you've successfully made that point though. Kevlar is an incredibly low-level form of protection that's usually only effective against handgun rounds... any rifle round would blow through Kevlar as well.

In other words you might as well have mentioned that crossbows can penetrate paper just as easily as a bullet could and went on to conclude that crossbows were as effective as firearms. Both Kevlar and paper armor are equally relevant to the modern battlefield... that is to say not very much at all.

Modern ceramic armor does mean all-around better resistance to all things, including traditional forms of attack. A crossbow bolt could pierce plate armor from the 14th century, but could not do so against modern equivalent armor.

I'd be okay with this if only knife users had to aim. Make it so that if you knife someone in an unprotected part of their body, you get a OHK. Otherwise they just get a hit indicator but receive no damage, so they can just turn around, laugh at you, and then shoot you in the face with a real weapon.

But with the lazy swipe system they have now, it's pretty obvious that there's not much aiming involved.

If only Infiltrator can backstab like Spy in TF2 and result in an insta - kill, since they can aim at weak spot of the shields and armor..