All of the armor slope advantages, the gun caliber, and other "facts" are irrelevant if you can't hit the other tank, and hit it FIRST. Pure gun caliber isn't the only meaningful statistic. That sloped armor comes at a distinct cost, which includes a far more cramped internal layout that's problematical for the crew. Situational awareness, reaction times, and reload times more often determine who wins a tank duel, not that tank duels were even the main cause of tank losses. In reality, AT Guns were the real tank killers. The game gives the Soviets the "raw stat" advantages which they had in reality, without penalizing them for the various other factors that allowed them to obtain those high numbers, which historically led to them losing a high number of tanks in engagement after engagement.
Yes, the first few times that the Germans encountered the latest new Soviet armored monsters, they had no idea how to stop them, and the new machines did surprisingly well. Once the Germans figured out their weaknesses and learned how to counter them, they weren't nearly as effective as the raw numbers would have you believe. A lot of Soviet tanks were destroyed without ever firing a shot, because the Germans spotted them first, reacted faster, and were more accurate on their first shots, then had faster reload times to place a second shot more accurately, if the first didn't do the job. The Soviets were less likely to fire first, were less likely to hit with their first shot (but were in many cases slightly more likely to kill a tank if they did hit it), and were less likely to survive long enough to take a second shot. Better command and control options (radios and intercoms that actually remained functional, and were audible in a moving tank) allowed German tank crews to cooperate and respond to changes in the situation as a group, rather than becoming effectively isolated as soon as the hatches were closed.
Those "other" factors are not represented in the silly tank game, so German tanks and gun values may have been unrealistically modified to produce more historically "realistic" end results, otherwise the game would be seriously unbalanced. Besides, "bigger gun = bigger shell; better explosives = faster shell; bigger X faster = more alpha. Soviets had a bigger shell, Germans had higher velocity from the SAME length of gun barrel due to better chemistry. Besides, the huge guns are irrelevant if you can't hit the target.
Of course, I'm probably violating the basic forum rule: "Never argue with a tankie". It's probably for similar reasons as the old phrase "Never argue with an idiot, because other people might not be able to tell which of you is the idiot."