I think there's a fundamental confusion at play here, none of the people are asking for a 'casual' experience, they want a 'realistic' and hard-core one. IRL, body armor at level 3 or above will save you from several rifle caliber shots, with bruising only for the first few.
On the other hand, the TTK should be lowered people seem to believe that a rifle bullet can one hit a person in heavy armor, which is incredibly unrealistic and would only make sense as a 'hardcore' experience if it was a WW2 or Vietnam Era game without any body armor whatsoever. Even one 9mm or .45 to the torso of an unarmored opponent isn't guaranteed to incapacitate, that's why IRL, police are trained to double tap armed suspects..
The game with the closest depiction of real body armor is Escape from Tarkov, which might be a little too much for my tastes, especially as we're playing as relatively poorly equipped forces. But if we had to shift the game, that's the direction it needs to shift from source insurgency.
I think the biggest reasons for a perceived too high TTK is the lack of reaction to getting shot, ideally a hit should cause massive aimpunch and sway to simulate the nasty bruise a stopped rifle shot will still produce. That will stop people from calmly turning around and headshotting you in turn, and make positioning and tactics all the more important!
Also, heavy armor could always be made a point more expensive, and slow users more, that isn't an issue of realism or hardcoreness at all, seeing as there all kinds of IRL body armors.
Also, now there's a use for proper sniper rifles for sniping as opposed to scoped ARs, as they're much more likely to guarantee a one hit kill at range.
Dont pretend like you are an army veteran that has survived multiple gun shot wounds and IED explosives...We all know you dont have any clue about what you are talking about. Nobody here wants a 1-to-1 real life experience military shooter. That's just plain dumb. We want the game to have the same fun core mechanics of the original insurgency (which is only a video game btw, not a real war simulator).
So i dont care whether armor can stop bullets in real life or not. I just want this new insurgency to have the same mechanics of the old game, with additional improvements like better graphics, better animations, more guns, more attachments, more maps...etc.