The efficacy of German armor is played up, but it's also that people tend to focus only on their big cats rather than their much more numerous assault guns, AT guns and earlier tank models (e.g. Pz III / IV) which statistically would provide the lion's share of kills against the allies. The idea of a single indomitable Tiger is menacing, but you were more likely to get killed by a hidden Pak somewhere or a PzIV.
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The early war german tanks and assault guns effectiveness was primarily due to tactics and blitzkrieg though. Not really the unit itself. Thats why even though they were inferior to the common allied tank, germans made really good use of them. As the war progressed, suddenly allies keep producing more and more tanks, logistics and supply are getting back in order, big offensives fail in russia. Suddenly another blitzkrieg can't be pulled off, its no surprise smaller amounts of bigger tanks with more armor and better guns are showing up. It's not myth that some tiger/panther crews were able to kill large amounts of tanks due to superior gun and armor. I'm gonna try not to ramble here.
TL
R, even though most of kills came from panzer3s/stugs and such, their success was due to tactics, as well as allies being pitifully weak at the beginning of the war. Germany needed stronger, more superior vehicles than the common allied tank. Because you couldn't outproduce america and russia combined, no way. Since germany was losing rapidly by 1943, I don't really think it is fair to say that the rushed into production panthers and king tigers were the wrong way to go, or would of been bad vehicles. Just that a lot of factors indirectly affected them in a negative way. Bombing, rushed production, lack of quality resources/enough resources.
If mechanical problems, lack of quality metals/fuel, didn't plague late war german vehicles they performed decently. Problems the allies really had no worry for.