The Brittish 2 pounder could penetrate 56~57.5mm of armor at a range of 500 yards, (it was the best light antitank gun at that time) which is more armor than the Pz4E-G had as front armor (they had 30-50mm thick armor plates, depending on which version). So this gun, just as it is in the game, were perfectly capable of knocking out Pz4´s frontal in real life.
Same thing with the 6 pounder: it could punch thru armor plating as thick as 81-83mm at a range of 500 yards. This gun can do it in the game, and in real life as well.
Both guns did suffer from one drawback though: neither one of them could use HE shells, these guns were firing antitank shells and nothing else, which is why tanks with these guns faired very poorly against German antitank guns.
The American tanks had gyrostabilized main guns starting with the M3 Lee/Grant. All tanks produced thereafter, had gyrostabilized guns which allowed them to be used whilst moving with good accuracy. The British designed tanks did not have it, until the Centurion arrived (but that tank is a non-WW2 tank really). Although in the case of the Americans, most tank crews choosed to not use the gyrostabilizing system since they thought it to be not much of use, and thus prefered the old method of stop-targeting-fire-move.
German tanks didnt have gyrostabilized guns, but of course these tanks could fire on the move as well, but by doing so, they lost all accuracy.
The Panther had 40-50mm (depending on which version, (Ausf D,A or G) we are talking about) and most, if not all guns of WW2 could knock it out by a flank shot. German crews were taught to always face the enemy with their thick frontal armor and by doing so, protect their tanks weaker sides. In other words, the Panther is just as vulnerable to flank shots in the game, as it was in WW2.
The accuracy, penetration, reloading time, etc of German guns is another thing: These has been nerfed down for the sake of balance in the game, and personally, I don´t like that kind of balance...
Also, guns in the vanilla version of MoW have two different settings: one for MP which tends to be more realistic, and another for SP which is highly unrealistic (boosted penetration etc).
~Zeke.
Ps.
I can´t belive that you´ve such problems with the Grant and/or Crusaders: usually they went up in flames as soon as I see them in the game... you must have some exceptional unluck when going up against these things...