The T-34 was indeed a marvel. It had the elegant Christie suspension, sloped armor, and a host of other clever features. But "most lethal tank" might be taking its success a bit far. There were a number of other tanks with more capable guns with better optics, certainly.

Also, while the T-34 was excellent, I am not sure that the USSR's engineering surpassed that of the other combatants you mentioned. The T-34 struck a good balance between mobility, lethality, and survivability, but other designs had their merits as well. The Tiger was outstanding while it was in contact with the enemy (which was admittedly rare, much like a vintage Alfa Romeo sports car it could be brilliant for very short stretches of time before inevitably breaking down). The Panther had some good design aspects as well.

On the Allied side, I find the Sherman to be unjustly maligned. Sure, it wasn't excellent when faced with other tanks, but it wasn't designed to fight other tanks. Design choices dictated that Tank Destroyers were supposed to fill the anti-armor role, while the Sherman was to be used for everything else. In the role it was designed for, the Sherman was excellent. It was much less expensive to produce than many other models, and was ubiquitous as a result. It had good range (not gun range, but how far it could go on a tank of fuel) and was easily repaired. Its armament was well suited for what it was designed to do--break through and get to attacking the enemy's weak rear as well as provide support for friendly infantry.

All of this is not to disparage the admitted excellence of the T-34's design. I merely submit that the design choices made by other WWII combatants do not mean that the engineering behind those efforts was not up to par.

I wouldn't call the T-34 "the most lethal" tank in WWII. During the early phase of the war, it was very unreliable and would break down quite often. Its engine needed repairs on average every 100 hours of operation. In practice this meant a lot of abandoned tanked on the roadside during the Soviet retreat. For comparison purposes, the Sherman was reliable for about 2000 hours.

Also the T-34 lacked many features of other tanks. It optics weren't good. Most T-34s lacked radios. If a T-34 caught on fire, its magazine was likely to detonate (unlike, say, the Sherman). The tank itself was cramped inside. And because there was only room for 2 people in the turret, the commander had to double as the gunner.

Later in the war, the T-34 was simply outclassed by the heavy German tanks such as the Panther and the Tiger. Soviet armor losses were often very high. For example, in one of the most famous tank battles of the war, the Battle of Prokhorovka, the Soviets lost many times as many tanks as the Germans.

T-34 was still a good tank, offering a good compromise between mobility, armor and firepower. That combination made it effective, particularly early in the war. However its biggest advantage was that it could be massed-produced cheaply and easily, thus enabling the Soviets to usually having a numbers advantage.

The T-34 was simply not the "most lethal tank in WW2," the Germans destroyed them in massive numbers.

Far more T-34s were destroyed during the war than any other tank.