the germans started out with blitzkrieg tactics and had comparably light and fast tanks, then as the war progressed came out with heavier and heavier tanks (as well as losing the ability to successfully blitz whole countries),
quoting the wikipedia:
Germany's armoured Panzer force was not especially impressive at the start of the war. Plans called for two main tanks: the Panzer III medium tank and the Panzer IV infantry tank. However, by the beginning of the invasion of Poland, only a few vehicles were available. As a result, the invasions of Poland and France were carried out primarily with the inferior Panzer I and Panzer II light tanks, with some cannon-armed light tanks from Czechoslovakia. As the war proceeded, production of the heavier tanks increased.
During the Operation Barbarossa, the German invasion of the Soviet Union in 1941, it was discovered that the Soviet T-34 tank outclassed the Panzer III and IV. Its sloped armour could defeat most German weapons, and its 76.2 mm gun could penetrate the armour of all German tanks. The Panzer III, which was intended to be the main medium tank, was upgraded to a longer, higher-velocity 50 mm gun. Even this was only marginally effective. Thus the Panzer IV, originally intended to be a support tank, became the de facto main medium tank re-armed with a long-barrelled, high velocity 75 mm gun. A new tank, the Panzer V Panther, was developed, incorporating lessons learned from the T-34. The Germans' traumatic experiences against the Soviet heavy tanks, with cases of single KV tanks holding up entire German tank units, spurred them to develop ever heavier designs including the Tiger and Tiger II Königstiger ("King Tiger").
As to the research, i think it is probably a good thing that they are going for a balance between HOI1 and HOI2 research styles.