Yeah, you could think about in this way: a soldier has two weapons, a submachine gun and a support anti-tank weapon (LAW or something like that). The submachine gun is an epitome of soft attack, the LAW is clearly designed for hard attack. By saying that hard attack should work as well against soft targets, you're effectively saying the soldier would do pretty well using the LAW instead of the submachine gun.
Yeah, pretty much - a direct hit of a LAW will kill an enemy soldier. With some luck, it will incapacitate nearby ones too, but since its explosive warhead is tailored for anti-tank use, it's not particularly effective with this "area of effect" business.
But there's never just one enemy. A shot from a LAW takes, I dunno, maybe ten to fifteen seconds to get off (edit: based on my own experience - I think that's how fast a good soldier does it. I'm way slower...). It can't be fired in bursts, so if you miss, you give your enemy precious seconds while you get another LAW ready to kill another soldier or three. Meanwhile, with the submachine gun, you could've downed maybe ten guys, and given them much less "free time" between your shots - constantly keeping them on their toes, which is a big asset in itself.
So all in all, this whole "flesh makes you immune to armour piercing" is just your misguided interpretation of what constitutes hard and soft attack. The attack values reflect not only whether you get instagibs on hit, but also aspects like rate-of-fire (very important against small individual targets like humans), accuracy, ability to provide cover, etc. Equipment good for hitting a large object so it leaves a big mark have good hard attack, equipment good for hitting multiple small objects has good soft attack, equipment good for both have good hard and soft attack. It's not like Doom where you just run around gibbing zombies with your BFG because you're maxed on energy cells.