German tank and aircraft design and logistics had their own issues that made things worse, but largely, the biggest issue was just not being capable of keeping up with American manufacturing and Russian willingness to throw bodies at the fight.
Just for context Allied tank production was 276k to the axis 67k. Most other production categories show similar ratios. Your tanks can be perfectly reliable, and superior in every way, but it will be hard to win a fight when you are outnumbered 4:1.
Even now, the emerging doctrine from Ukraine, and now Iran, is to fight using asymmetric production advantages. Ukraine is taking out multimillion dollar facilities and ships with five figure UAVs. Iran has depleted US air defense stocks costing billions with a few million dollars worth of drones powered by motorcycle engines.