The Germans did not have a choice but to lower the quality of parts going into the Panther, the raw materials and time for the good stuff was not there. Not helped by French workers actively sabotaging stuff. Littlefields crew found WWII cigarette butts in the final drives when they disassembled them. I wonder how much was due to technical design, how much due to lack of high quality parts and how much to sabotage?
There simply was not enough time to properly develop the vehicle. e.g. the undersized gearbox. It was driving on its own out the factory and was able to shoot the cannon? There is the frontline! Go!
But to which percentages faults can be attributed to the causes, we can only make wild guesses.
The gearbox might have fared better had they not decided to slap another 10 tons of armor onto the vehicle after they designed it.
I think a good analogue for the Panther is to think about how a Sherman Jumbo Firefly might have fared in WW2 and whether it would have been better than what was actually fielded.