They actually did standardize pretty quickly. Panzer III and Panzer IV were the workhorses in Russia, paired up with the StuG (which used the Pz III chassis). I think that it's arguable that no production strategy could have led to German success. Had they tried to produce T-34 or Sherman type tanks (and the Panther was kind of intended to be that tank), they still would have been overwhelmed by the sheer number of tanks built buy the Allies. The Soviets at their peak year produced over 29K tanks, with the US contributing around 21K. The Germans maxed out at around 8k.

IMHO, the Soviets alone could have eventually defeated Germany, thought at much greater cost (as if over 20m casualties wasn't already incredible).