Some Fallout lore questions...

[Atomic Postman]

But the thing is that ingame PA is extremely powerful. It reduces all damage by at least 10 and then reduces the remaining damage by at least 40%.

If we look at the game's weapon damage, we can see how powerful PA really is. It makes the vast majority of weapons in the game cause no or very little damage (between 0 and less than 10 per attack/round). It also protects the wearer from the most powerful weapons:

• Mega Power Fist damage is 20 to 40. With a PA that damage becomes 4.8 to 16.8.
  
• Super Sledge damage is 18 to 36. With a PA that damage becomes 3.6 to 14.4.
• PPK12 Gauss Pistol damage is 22 to 32. With a PA that damage becomes 6 to 12.
• H&K G11E damage is 13 to 23. With a PA that damage becomes 0.4 to 6.6.
• M72 Gauss Rifle damage is 32 to 43. With a PA that damage becomes 12 to 18.6.
• Pancor Jackhammer damage is 18 to 29. With a PA that damage becomes 3.6 to 10.2.
• Bozar damage is 25 to 35. With a PA that damage becomes 7.8 to 9.2.
• Improved Flamer damage is 45 to 90. With a PA that damage becomes 13.2 to 31.2.
• Rocket Launcher damage is 35 to 100. With a PA that damage becomes 7.5 to 40.
• Alien Blaster damage is 30 to 90. With a PA that damage becomes 10.8 to 46.8.
• YK42B Pulse Rifle damage is 54 to 78. With a PA that damage becomes 25.2 to 39.6.
• Plasma Grenade damage is 40 to 90. With a PA that damage becomes 18 to 48.
• Plastic Explosives damage is 40 to 80. With a PA that damage becomes 10 to 30.

And this is without counting the Hardened version.

PA is extremely powerful ingame. But it's far from being as protective as a tank. I think that what confused people was that when the Fallout Bible mentions PA as a tank, it means being able to pack a punch as a tank (like that quote I posted before shows). Being able to blast defenses using heavy weaponry. It also still provides good protection to the wearer (most if not all low caliber weaponry can't really damage the wearer), just not like an actual tank.
I don't know why people saying PA is a tank buggers me so much... Maybe it's because I was in the artillery and armored division when I was in the army.

It's a semantics thing I guess. I'm pretty sure I've referred to PA being "like a tank" in the past but I never meant it literally. If PA had the stopping power of tank armor the BoS would literally never lose.