I'm not sure what game you're playing. I suppose since you've never actually used the PTRD in-game, so you imagine that it somehow can take out PzIV and PzIII with "one shot to the front." This is simply not the case. A skilled gunner can take out a PzIV or PzIII with one shot to the side, but only if he hits the ammo storage. There is nothing unrealistic about this. The PTRD could penetrate side armor on both those tanks, and if a very large, fast-moving bullet hits a bunch of shells filled with explosives, bad things will ensue. Interestingly, the PTRD has just barely enough penetration to penetrate a Panther from the side (Panther has relatively little armor on the side compared to front, unlike Tiger, which is very thick all around), though not reliably and only at a perfect angle. In game, this seems to be reflected fairly well - in practice mode, I need about 10 perfect 90 degree shots from about 5 feet away to the ammo box in order to destroy a Panther (and I know exactly where that ammo box is), so in-game this would be very rare.
Also, this stuff about the Panzerfaust doesn't really happen in game from what I've observed. The PF seems to take 2 shots with all tanks, but sometimes destroys them in 1. Realistically, if the PF strikes something like the tracks or the road wheels, it probably wouldn't actually penetrate the tank due to the nature of the shaped charge - all of the force would be sent into the wheel or track, destroying it, but not actually reaching the hull. Likewise, no weapon is 100% reliable, though it does seem like it *consistently* takes two shots, which seems quite odd.